Chronic toxic effects of supermethrin on some biochemical parameters (AST, ALT, LDH, creatinine and total proteins) were investigated in 84 individuals of Japanese quail divided into four groups (control-K, experimental group I-P1, experimental group II-P2, experimental group III-P3) in the conditions of 140-day avian reproductive test. The three experimental groups received the tested substance at these doses: P1-10.7 mg/kg l.w./day, P2-21.4 mg/kg l.w./day, P3-35.7 mg/kg l.w./day. The results of observation of the enzyme activities AST and ALT show that only the AST activity (in the course of 140-day avian reproductive test) significantly increased to 1.225 mu kat/l in the females of experimental group P1, to 1.053 mu kat/l in P2 and to 1.014 mu kat/l in P3 against the control, in which the AST activity was 0.670 mu kat/l. The values of AST activity in the males were 1.143 mu kat/l in P1, 1.117 mu kat/l in P2 and 1.090 mu kat/l in P3 against the control 0.8395 mu kat/l. The investigation of variations in total LDH activity in Japanese quail after 140-day avian reproductive test has shown an increase in the LDH activity in the males (11.193 mu kat/l in P1, 11.269 mu kat/l in P2, 8.245 mu kat/l in P3 and 7.362 mu kat/l in K) as well as in the females (10.91 mu kat/l in P1, 12.023 mu kat/l in P2, 10.196 mu kat/l in P3 and 7.055 mu kat/l in K).(ABSTRACT TRUNCATED AT 250 WORDS)