['To explore the effect of the phytoestrogen daidzein on the growth and development of the testis and epididymis in male SD rats.', 'Thirty 10-week old (early adult) and 30 4-week old (pubertal) male SD rats were included in the study, each age group equally divided into 5 subgroups: normal control, positive control, low-dose, medium-dose and high-dose. The normal and positive control groups were given 1 ml distilled water and the same amount of distilled water containing diethylstilbestrol (DES) at the dose of 0.1 mg/kg, and the low-, medium- and high-dose groups administered daidzein in the dose of 2mg/kg, 20 mg/ kg and 100 mg/kg, respectively, all by gavage for 90 days. Observations were made on the changes in body weight and testicular and epididymal indexes, as well as on the structural changes of the testis and epididymis by H&E staining.', 'The early adult rats showed no significant differences in body weight and testicular and epididymal indexes between the claiclzein groups and the control (P > 0.05), nor did the pubertal rats in epididymal index (P > 0.05). The testicular index differed significantly between the high-dose group (3.21 +/- 0.07) and the normal control (3.71 +/- 0.45) (P < 0.05). The body weight reduced markedly in the high-dose group (P < 0.05), but with no significant differences between the normal control and the other two dose groups (P > 0.05). No obvious changes were observed in epididymal morphology in all the daidzein groups of the early adult and pubertal rats, but high-dose daidzein resulted in smaller testes and impaired spermatogenesis.'] Does [ High-dose daidzein affect growth and development of reproductive organs in male rats ]?