A biochip assembly comprising: a plurality of enclosed elongate microchannels, each microchannel having an inlet port adjacent one of its proximal and distal ends; and an outlet port adjacent its other end; a plurality of reservoir wells for use with the microchannels; an enclosed liquid delivery channel assembly having two or more combined inlet and outlet ports, at least one forming an inlet port and at least one other forming an outlet port; and an enclosed sample holder transfer assembly for connecting a port of one part of the biochip assembly to a port or reservoir well of another part and for connecting two reservoir wells together, characterised in that the biochip assembly comprises: a main support frame comprising a base frame and an upper frame mounting between them a plurality of separate and removable biochip modules (15, 16, 17), namely an input module forming the enclosed liquid delivery channel assembly, at least one reservoir well containing module and a microchannel containing module and in which the enclosed sample holder transfer assembly comprises a pair of support plates; a plurality of rigid tubes mounted on each support plate for engagement with the modules (15, 16, 17) and with transfer conduits for connecting a rigid tube on one support plate with a rigid tube on the other support plate, and the upper frame mounts upstanding posts having slots for reception of the support plates, and releasable connection means for mounting the sample holder transfer assembly. a plurality of enclosed elongate microchannels, each microchannel having an inlet port adjacent one of its proximal and distal ends; and an outlet port adjacent its other end; a plurality of reservoir wells for use with the microchannels; an enclosed liquid delivery channel assembly having two or more combined inlet and outlet ports, at least one forming an inlet port and at least one other forming an outlet port; and an enclosed sample holder transfer assembly for connecting a port of one part of the biochip assembly to a port or reservoir well of another part and for connecting two reservoir wells together, characterised in that the biochip assembly comprises: a main support frame comprising a base frame and an upper frame mounting between them a plurality of separate and removable biochip modules (15, 16, 17), namely an input module forming the enclosed liquid delivery channel assembly, at least one reservoir well containing module and a microchannel containing module and in which the enclosed sample holder transfer assembly comprises a pair of support plates; a plurality of rigid tubes mounted on each support plate for engagement with the modules (15, 16, 17) and with transfer conduits for connecting a rigid tube on one support plate with a rigid tube on the other support plate, and the upper frame mounts upstanding posts having slots for reception of the support plates, and releasable connection means for mounting the sample holder transfer assembly. a main support frame comprising a base frame and an upper frame mounting between them a plurality of separate and removable biochip modules (15, 16, 17), namely an input module forming the enclosed liquid delivery channel assembly, at least one reservoir well containing module and a microchannel containing module and in which the enclosed sample holder transfer assembly comprises a pair of support plates; a plurality of rigid tubes mounted on each support plate for engagement with the modules (15, 16, 17) and with transfer conduits for connecting a rigid tube on one support plate with a rigid tube on the other support plate, and the upper frame mounts upstanding posts having slots for reception of the support plates, and releasable connection means for mounting the sample holder transfer assembly.