Micro-enzyme sensors using L-amino acid oxidase (EC 1.4.3.2) and D-amino acid oxidase (EC 1.4.3,3) were developed for measuring L- and D-amino acids. The platinum micro-sensors (platinum diameter 30 mum) were etched in hot aqua regia to create a cavity at the tip. A porous composite material prepared from acetylene black and Teflon emulsion was packed into the tip of the platinum micro-sensors and the redox mediator [Os(bpy)3](PF6)2 was monitored by cyclic voltammetry in the potential range 200-900 mV. The micro-sensors were dipped overnight in buffer solution containing the desired enzyme to immobilize it on the tip by the adsorption method. Calibration graphs for measurements of L- and D-amino acids. the effects of pH. temperature and concomitant compounds, the lifetime of the micro-sensors and their availability for measuring L-amino acids in urine were examined. Under optimal conditions, the response of the sensors was linear in the concentration ranges 3.3-20 mg l-1 for L-amino acids and 0.83-17 mg l-1 for D-amino acids.