diff --git a/src/kyupy/circuit.py b/src/kyupy/circuit.py
index cacc5b5..b81904a 100644
--- a/src/kyupy/circuit.py
+++ b/src/kyupy/circuit.py
@@ -314,6 +314,41 @@ class Circuit:
     def get_or_add_fork(self, name):
         return self.forks[name] if name in self.forks else Node(self, name)
 
+    def substitute(self, node, impl):
+        """Replaces a given node with the given implementation circuit.
+
+        The given node will be removed, the implementation is copied in and
+        the signal lines are connected appropriately. The number and arrangement
+        of the input and output ports must match the pins of the replaced node.
+        """
+        node_in_lines = [l for l in node.ins if l]
+        node_out_lines = [l for l in node.outs if l]
+        impl_in_lines = [n.outs[0] for n in impl.io_nodes if len(n.outs) > 0]
+        impl_out_lines = [n.ins[0] for n in impl.io_nodes if len(n.ins) > 0]
+        assert len(node_in_lines) == len(impl_in_lines)
+        assert len(node_out_lines) == len(impl_out_lines)
+        in_lines_map = dict(zip(impl_in_lines, node_in_lines))
+        out_lines_map = dict(zip(impl_out_lines, node_out_lines))
+        node.remove()
+        node_map = dict()
+        ios = set(impl.io_nodes)
+        for n in impl.nodes:
+            if n not in ios:
+                node_map[n] = Node(self, node.name + '~' + n.name, n.kind)
+        for l in impl.lines:
+            if l in in_lines_map:
+                ll = in_lines_map[l]
+                ll.reader = node_map[l.reader]
+                ll.reader_pin = l.reader_pin
+                ll.reader.ins[ll.reader_pin] = ll
+            elif l in out_lines_map:
+                ll = out_lines_map[l]
+                ll.driver = node_map[l.driver]
+                ll.driver_pin = l.driver_pin
+                ll.driver.outs[ll.driver_pin] = ll
+            else:
+                Line(self, (node_map[l.driver], l.driver_pin), (node_map[l.reader], l.reader_pin))
+
     def copy(self):
         """Returns a deep copy of the circuit.
         """
diff --git a/src/kyupy/techlib.py b/src/kyupy/techlib.py
index 5e8e843..f8b3a19 100644
--- a/src/kyupy/techlib.py
+++ b/src/kyupy/techlib.py
@@ -1,5 +1,5 @@
 from .circuit import Node, Line
-
+from . import bench
 
 def add_and_connect(circuit, name, kind, in1=None, in2=None, out=None):
     n = Node(circuit, name, kind)
@@ -66,6 +66,23 @@ class TechLib:
         if 'MUX' in kind and pin == 'S': return False
         return pin in ('Q', 'QN', 'Z', 'ZN', 'Y', 'CO', 'S', 'SO', 'C1')
 
+    @staticmethod
+    def substitute_nonsim_cells(circuit):
+        tmap = {'ISOLAND': bench.parse('input(iso, d) output(q) not_iso=not(iso) q=and(not_iso, d)'),
+                'AO221'  : bench.parse('input(in1, in2, in3, in4, in5) output(q)  a=ao22(in1, in2, in3, in4) q=or(a, in5)'),
+                'AOI221' : bench.parse('input(in1, in2, in3, in4, in5) output(qn) a=ao22(in1, in2, in3, in4) qn=nor(a, in5)'),
+                'OA221'  : bench.parse('input(in1, in2, in3, in4, in5) output(q)  a=oa22(in1, in2, in3, in4) q=and(a, in5)'),
+                'OAI221' : bench.parse('input(in1, in2, in3, in4, in5) output(qn) a=oa22(in1, in2, in3, in4) qn=nand(a, in5)'),
+                'AO222'  : bench.parse('input(in1, in2, in3, in4, in5, in6) output(q)  a=ao22(in1, in2, in3, in4) q=ao21(in5, in6, a)'),
+                'AOI222' : bench.parse('input(in1, in2, in3, in4, in5, in6) output(qn) a=ao22(in1, in2, in3, in4) qn=aoi21(in5, in6, a)'),
+                'OA222'  : bench.parse('input(in1, in2, in3, in4, in5, in6) output(q)  a=oa22(in1, in2, in3, in4) q=oa21(in5, in6, a)'),
+                'OAI222' : bench.parse('input(in1, in2, in3, in4, in5, in6) output(qn) a=oa22(in1, in2, in3, in4) qn=oai21(in5, in6, a)'),
+                }
+        for n in list(circuit.nodes):
+            for k, v in tmap.items():
+                if n.kind.startswith(k):
+                    circuit.substitute(n, v)
+
     @staticmethod
     def split_complex_gates(circuit):
         node_list = circuit.nodes
diff --git a/tests/test_circuit.py b/tests/test_circuit.py
index 8eb4e01..64da48c 100644
--- a/tests/test_circuit.py
+++ b/tests/test_circuit.py
@@ -1,7 +1,8 @@
 import pickle
 
 from kyupy.circuit import Circuit, Node, Line
-from kyupy import verilog
+from kyupy import verilog, bench
+from kyupy.techlib import TechLib
 
 def test_lines():
     c = Circuit()
@@ -104,9 +105,26 @@ def test_circuit():
 
 
 def test_pickle(mydir):
-    c = verilog.load(mydir / 'b14.v.gz')
+    c = verilog.load(mydir / 'b15_4ig.v.gz')
     assert c is not None
     cs = pickle.dumps(c)
     assert cs is not None
     c2 = pickle.loads(cs)
     assert c == c2
+
+def test_substitute():
+    c = bench.parse('input(i1, i2, i3, i4, i5) output(o1) aoi=AOI221(i1, i2, i3, i4, i5) o1=not(aoi)')
+    assert len(c.cells) == 2
+    assert len(c.io_nodes) == 6
+    aoi221_impl = bench.parse('input(in1, in2, in3, in4, in5) output(q) a1=and(in1, in2) a2=and(in3, in4) q=or(a1, a2, in5)')
+    assert len(aoi221_impl.cells) == 3
+    assert len(aoi221_impl.io_nodes) == 6
+    c.substitute(c.cells['aoi'], aoi221_impl)
+    assert len(c.cells) == 4
+    assert len(c.io_nodes) == 6
+
+    c = bench.parse('input(i1, i2, i3, i4, i5) output(o1) aoi221=AOI221(i1, i2, i3, i4, i5) o1=not(aoi221)')
+    assert len(c.cells) == 2
+    TechLib.substitute_nonsim_cells(c)
+    assert len(c.cells) == 3
+    print('\n'.join(map(str, c.nodes)))
\ No newline at end of file