The aim of this study was to assess the impact of di(n-butyl) phthalate (DBP) on the rat’s prepubertal testis. Male Wistar rats were given daily subcutaneous injections with DBP (20 or 200 μg) or a vehicle from the 5th to the 15th postnatal day (pd). On the 16^th pd, the rats were euthanized, and the testes were dissected, weighed, and paraffin embedded. The blood was collected to determine the serum levels of testosterone (T), estradiol (E) and FSH. The following parameters were assessed in the testis sections: diameter and length of seminiferous tubules (st), numbers of spermatogonia A + intermediate + B (A/In/B), preleptotene spermatocytes (PL), leptotene + zygotene + pachytene spermatocytes (L/Z/PA) and Sertoli cells per testis, percentage of st containing gonocytes or pachytene spermatocytes or lumen. An estrogenicity in vitro test was performed by means of a transgenic yeast strain expressing human estrogen receptor alpha. At both doses, DBP had no influence on testis and seminal vesicle weight, st diameter and length, number of germ and Sertoli cells per testis, percentage of st containing gonocytes or pachytene spermatocytes or lumen. DBP did not change E, T or FSH serum levels. The in vitro yeast screen showed that DBP was a weak estrogenic compound, approximately six to seven orders of magnitude less potent than 17β-estradiol. In conclusion, exposure of a rat to DBP in doses 100 or 1,000-fold higher than a Tolerable Daily Intake for humans had no effect on its testicular development. (Folia Histochemica et Cytobiologica 2011; Vol. 49, No. 4, pp. 685–689) The aim of this study was to assess the impact of di(n-butyl) phthalate (DBP) on the rat’s prepubertal testis. Male Wistar rats were given daily subcutaneous injections with DBP (20 or 200 μg) or a vehicle from the 5th to the 15th postnatal day (pd). On the 16^th pd, the rats were euthanized, and the testes were dissected, weighed, and paraffin embedded. The blood was collected to determine the serum levels of testosterone (T), estradiol (E) and FSH. The following parameters were assessed in the testis sections: diameter and length of seminiferous tubules (st), numbers of spermatogonia A + intermediate + B (A/In/B), preleptotene spermatocytes (PL), leptotene + zygotene + pachytene spermatocytes (L/Z/PA) and Sertoli cells per testis, percentage of st containing gonocytes or pachytene spermatocytes or lumen. An estrogenicity in vitro test was performed by means of a transgenic yeast strain expressing human estrogen receptor alpha. At both doses, DBP had no influence on testis and seminal vesicle weight, st diameter and length, number of germ and Sertoli cells per testis, percentage of st containing gonocytes or pachytene spermatocytes or lumen. DBP did not change E, T or FSH serum levels. The in vitro yeast screen showed that DBP was a weak estrogenic compound, approximately six to seven orders of magnitude less potent than 17β-estradiol. In conclusion, exposure of a rat to DBP in doses 100 or 1,000-fold higher than a Tolerable Daily Intake for humans had no effect on its testicular development. (Folia Histochemica et Cytobiologica 2011; Vol. 49, No. 4, pp. 685–689)