Phthalates are chemicals used in many industrial products (plastic toys, shampoos, soaps), and are suspected of inducing adverse effects on the male reproductive system. In the present study, we evaluated the effects of the plasticizer di-(2-ethylhexyl)-phthalate (DEHP) on the reproductive function and sexual behavior of male offspring rats, exposed in utero and during lactation (0, 20, 100 and 500 mg/kg per day by gavage). The effects produced clearly demonstrate the ability of DEHP to disrupt the androgen-regulated development of the male reproductive tract. Absolute and relative weights of androgen-dependent tissue organs (ventral prostate and seminal vesicle) were significantly reduced at the highest dose level tested (500 mg/kg per day). Impairment of male sexual behavior (500 mg/kg per day) was also observed. Moreover, the reduction in daily sperm production and epididymal sperm counts observed after administration of the highest dose suggests an impairment of the spermatogenic processes. Most of the adverse effects reported here were observed both during puberty and during adulthood, indicating permanent effects of in utero and lactational DEHP exposure.