The influence of single oral dose of anti-inflammatory, antipyretic and analgesic agents on urinary enzymes was investigated in rats as a indicator of nephrotoxic effect. Urinary LDH activity was significantly elevated by aspirin, ketophenylbutazone, aminopyrine, phenacetin and acetaminophen. These drugs increased also H/M ratio of LDH isoenzymes. Although other test drugs have no effect on LDH in urine phenylbutazone and indomethacin elevated GPT and A1-P, oxyphenbutazone did gamma-GT and anthranilic acid derivatives did Al-P and gamma-GT. Other drugs such as sodium salicylate, ibufenac, ibuprofen, bucolome, aminopropylone, sulfinpyrazone, benzydamine and mepirizole did not significantly influence any enzyme activities measured in urine.