A novel electrochemical microbiosensor for protein determination based on an all-solid-state microelectrodes with a Ppy [3,3-Co(1,2-C2B9H11)2] solid internal contact and immobilized trypsin and carboxypeptidase B was developed. The specificity of the sensor signal was investigated using artificial ester and amide substrates of the proteinases: N[alpha]-benzoyl-l-arginine ethyl ester hydrochloride (BAEE), N[alpha]-benzoyl-dl-arginine-p-nitroanilide hydrochloride (BAPNA), and Hippuryl-Arg. Study on a possibility of protein detection showed that quantitative proteins determination can be performed with the microbiosensor in the concentration range of 1-60 [mu]g/ml.