The aim of the experimental work described in this thesis was to investigate the effects of a ubiquitous environmental contaminant, the synthetic platiciser Di-butylphthalate (DBP) on the developing male reproductive tract. Observed changes were compared to those evident in the human males Testicular dysgenesis syndrome (TDS), which is increasing in incidence. To investigate whether DBP treatment induced any TDS-like changes, pregnant rats were gavaged daily with DBP at doses up to 500mg/kg/day from embryonic (e) day e13.5 up to e21.5. Morphological and hormonal parameters (testosterone, inhibin-B) were then assessed in male rats aged e21.5 or in adulthood ± in utero DBP exposure. Concurrently, untreated fetal rat and fetal human testis explants were cultured in vitro ± MBP (Mono-butylphthalate), the DBP metabolite, at levels of up to 1mM, to investigate whether the array of adverse effects seen with the in utero compared ± MBP exposure. The in vitro experiments were restricted to 48h exposure duration, so an additional in vivo treatment regime was established to compare the endopoints induced after just 48h exposure to DBP in utero. Pregnant rats were dosed daily by gavage with 500mg DBP/kg/day on e19.5 and e20.5 only. Morphological and hormonal parameters (testosterone, inhibin-B) were then assessed in male rats aged e21.5 ± 48h. Findings were compared with those from the original in utero studies in which DBP exposure spanned the period e13.5-e20.5. The long-term in utero exposure regime induced an array of changes in the phenotype of the male reproductive tract, evident in e21.5 and adult animals, including testis maldescent (cryptorchidism) and reduced fertility. Changes in testis morphology such as alteration in the distribution of Leydig cells and induction of multinucleated gonocytes at e21.5 were also seen. The production of testosterone in testes at e21.5 was also significantly reduced following the DBP treatment, including a significant reduction in the protein expression levels of the steroidogenic enzyme P450scc. The short-term in utero exposure to DBP regime induced a generally less severe array of changes in the testis at e21.5 male reproductive tract than those seen after 8-day in utero DBP exposure. However, a greater reduction in testis testosterone was seen after short-term exposure than long-term exposure induced, despite less of a reduction in the expression of the steroidogenic protein P450scc. The precise mechanism through which DBP induces its array of developmental abnormalities is still unclear but these studies support the hypothesis that even short term in utero exposure to DBP directly affects the developing testis, probably by acting on Leydig cells and disrupting normal testis endocrinology.