We present a technology for the fabrication of three dimensional microfluidic channels in optically transparent substrates consisting of polymers with different properties. The microstructures are fabricated using polymer replication techniques with a view to the production of microfluidic devices with characteristics suitable for biomedical applications. The replication processes can be used to fabricate large numbers of highly precise, complex microchannels via replication from a single similarly precise master, containing microstructures fabricated from silicon-based materials using lithographic micromachining techniques. Silicon oxide and silicon nitride-based masters have been used, due to their anti-adhesion properties, to produce microchannels, in the transparent polymers, that are suitable for channel profiling measurements and optical studies of fluid flow. (c) 2005 Elsevier B.V. All rights reserved.