there are three main classes of electrochemical microbiosensors based on silicon chip, namely conductimetric, amperometric and potentiometric (i.e. fet). a brief account of the detection principle, fabrication and mode of operation of the first two types of microbiosensors with specific clinical applications is presented. these sensors are essentially based on serpentined parallel metal tracks on silicon dioxide on a silicon substrate where a biological sensing layer reacts with the test species. it is expected that the miniaturised conductimetric urea biosensor device and associated instrumentation will find applications, e.g. in the analysis of urea for in vitro blood analysis, in renal surgery and in dialysis monitoring. this device also offers potential for the measurement of many other biological substances when their complementary enzymes are immobilised across the surface of the electrical conductor networks on the silicon chip. the feasibility of constructing multianalyte micro-amperometric biosensors that are both highly selective and simple to operate has been demonstrated for the simultaneous analyses of clinical glucose and galactose