Abstract: A biochip assembly (1) is provided for cell based and other assays. A main support frame (11) releasably mounts separate and removable biochip modules (15, 16(a), 17 and 16(b)). There is an input module (15) which forms an enclosed liquid delivery assembly for connection to a liquid pump. There are two reservoir containing modules (16(a)) and (16(b)) having sets of wells (33(a); 33(b); 33(c); and 33(d); 33(e); 33(f)) respectively, which reservoir containing modules (16(a)) and (16(b)) are on either side of a microchannel containing module (17) which has an input port (35) and output port (36) for each of a plurality of microchannels (37). A removable transfer assembly (18), shown connecting the input module (15) and the reservoir containing modules 16(b), is used to interconnect the modules; to store liquid; to aspirate liquid from and deliver to the wells (33); and to delivery liquid through the microchannels (37).