Abstract: Following pretreatment of adult male rats with contragestational agent 3-(2-ethylphenyl)-5-(3-methoxyphenyl)-1H-1, 2, 4 triazol (DL-111-IT) 80mg/kg/d for 4 consecutive days, the liver weight of the animals and the ability of its reduced hepatic cytochrome P-450 to form complex with metyrapone or the metabolic intermadiate (MI) of tert-butyl p-aminobenzoate remained unchanged or declined. In contrast, the hepatic cytochrome P-450 increased to 1.5 fold of control value. The absorption peak of reduced cytochrome P-450-CO binding spectrum was hypsochromicly shifted, and the microsomal AHH activity as well as the UDP Glucuronosyltransferase activity toward l-naphthol were significantly enhanced. According to these observations, DL-111 IT may be considered a new polycyclic aromatic hydrocarbon type inducer of the drug metabolizing enzymes.