The aim of this paper was to examine if puromycin (PUR) and bacitracin (BAC) which delay the degradation of enkephalins (ENK) in vitro by the inhibition of aminopeptidases activity, may induce antinociceptive effects. Male Wistar rats were used. PUR in a dose of 100, 200 or 400 micrograms or BAC in a dose of 10, 25, 50 micrograms were administered intracerebroventricularly in conscious animals. As an antagonist of ENK, naloxone (NAL) was used in doses of 1, 5, 10 or 20 mg/kg ip. Antinociceptive effect was measured by the method of hot-plate. The level of ENK in the striatum was examined by biological method using mice vas deferens. PUR induced the dose-related analgesic effect abolished by NAL and increased the level of ENK in the striatum. BAC also elicited the dose-related antinociceptive effect and the increase of striatal concentration of ENK. But antinociceptive effect of BAC was not antagonized but potentiated by NAL. Moreover BAC evoked abnormal behavior of rats, namely the episodes of catalepsy and of barrel rotation. It is concluded that: PUR, but not BAC, is a useful pharmacological tool for the aminopeptidase inhibition and for activation of enkephalinergic neurons; aminopeptidases are concerned with activities of opioid peptides.