Experiments involving 118 prepubertal gilts (150-180 days old) were conducted to evaluate the effect of vitamin administration on reproductive tract development and ovarian responsiveness to exogenous gonadotropins. In Experiment 1 prepubertal Duroc gilts were assigned to two groups and injected or not with vitamins and Se and 14 days later given 600 IU PMSG and 200 IU hCG. Gilts were slaughtered on day 7 post oestrus detection. Vitamins and Se increased the length (P<0.05) but not the weight of the uterus and ovaries. The number of corpora lutea decreased (P<0.001) but their size increased (P<0.01) in the vitamin- and Se-treated group when compared to controls. In Experiment 2 gilts were injected with vitamins and Se as described in Experiment 1 ten days before PMSG/hCG and the treated gilts were injected again with vitamins and Se four days prior to the expected onset of the second oestrus. Gilts that did not express signs of the second oestrus after treatment were slaughtered on day 27 post onset of the first oestrus. Gilts given vitamins and Se had heavier and longer uteri (P<0.01) and a lower number of corpora albicans (P<0.01) in the previouoestrous cycle. The relatively high number of corpora albicans found both in control (26.5±3.1) and vitamin-treated (34.1±2.3) gilts after PMSG/hCG injection in Experiment 2 indicates an inconsistent response of prepubertal gilts to gonadotropins. We concluded that vitamin- and Se-flushing led to the formation of lower in number but larger in size corpora lutea after ovulation probably due to the progression of a smaller number of follicles to the ovulatory stage. Vitamins and Se increased the development of the uterus but did not influence the number of piglets at farrowing.