This study was designed to determine if prenatal exposure to oleic acid would alter testicular endocrine functions in either an estrogenic or antiandrogenic manner at puberty. Gravid dams were distributed into four groups of five rats each as follows: Control group (1 ml/kg olive oil throughout pregnancy), pre-treatment group (1000 mg/kg of oleic acid for 7 days before mating), preimplantation group (1000 mg/kg of oleic acid for the period of preimplantation), Organogenesis group (1000 mg/kg of oleic acid for the period of organogenesis). Dams delivered naturally and male offspring were studied into puberty. Morphological landmarks, hormone levels and sex accessory gland development were assessed. Estrogenic properties included shortened AGI, decrease in serum LH and T (P<0.001), increase in prolactin level in the organogenesis group. Antiandrogenic properties included delayed pubertal maturation, altered serum LH and T levels (P<0.001), epididymal sperm numbers in all treated groups. The results provide in vivo example of a pronounced degree of target tissue selectivity to an environmental endocrine-disruptor.