Effect of DL-111, 3-(2-ethylphenyl)-5-(3-methoxyphenyl-1H-1,2,4-triazole, a non-hormonal postimplantational antifertility agent, on testicular and accessory reproductive organ weights and total protein, RNA and DNA concentrations were evaluated in immature and adult rats. Treatment of 21-day-old rats at doses of 2.5 mg and 5 mg/kg body weight decreased body weight, weights of testes and accessory glands of reproduction. RNA and protein concentrations decreased significantly with significant increase increase in DNA concentration in testes, epididymis, ventral prostate and seminal vesicles. DL-111 treatment of adult rats at doses of 5 mg and 10 mg/kg body weight had no effect on body weight, but significantly decreased weights of testes and accessory glands of reproduction. RNA and protein concentrations decreased significantly in all tissues studied while DNA concentration was not altered. RNA/DNA ratio decreased significantly, reflecting ribosomal loss and cytoplasmic shrinkage. These effects of DL-111 are comparable to post-castrational changes in accessory glands of reproduction. We presume that these changes are mediated by blocking the androgen biosynthesis and/or by interfering with normal function of hypothalamo-pituitary-gonadal axis.