Penicillin sensitive enzyme electrodes were prepared on the basis of native penicillinase (EC 3.5.2.6) and penicillinamidase (CE 3.5.1.11), as well as penicillinase entrapped in a complex of polyethylenimine and polyacrylic acid or linked with albumin and lattice entrapped penicillinase. The time of the electrode response is 2-10 minutes. The electrode potential change within a minute is linear at 1-20 mM of benzylpenicillin and depends on the electrode type. The electrodes prepared on the basis of the native enzymes lost their sensitivity within the first 10 days. Sensitivity of immobilized penicillinase did not change for 15 days. The electrodes prepared on the basis of albumin-linked penicillinase preserved their high stability for 60 days. The sensitivity of these electrodes is slightly dependent on the phosphate buffer concentration (from 0.001 to 9 mM).