In this study specific activities of four acid glycosidases: beta-N-acethylhexosaminidase (beta-HEX), beta-galactosidase (beta-GAL), alpha- and beta-mannosidase (alpha- and beta-MAN) were investigated in Japanese quail testes and epididymides during posthatch development and regression after light reduction. The specific activity of testicular beta-HEX and beta-GAL increased steadily during posthatch development and assumed maximum values for testes weighing 200-400 mg, when numerous spermatocytes appear in the testes of quail, and then decreased slowly. These enzymes showed much higher specific activity after 15 days of light reduction, and decreased to the control level after 30 days. Activity of alpha- and beta-MAN remained rather constant during testicular development and involution. The epididymal activity of the acid glycosidases was very low in immature individuals, whereas in sexually mature birds it was found to increase several-fold. Short photoperiod resulted in a decreased activity of these enzymes after 30 days to the values found in immature birds. A marked increase in the activity of acid glycosidases in the epididymides of sexually mature animals and a decrease in this activity during epididymidal regression indicate that these enzymes take part in reproductive processes. It is concluded that the activities of beta-HEX, beta-GAL, alpha- and beta-MAN in the development and regression of Japanese quail testes and epididymides change similarly as in mammals.