A wide range of environmental pollutants commonly termed endocrine disrupters (ED) can mimic steroid hormones causing adverse health effects. Recent studies showed that bisphenol A (BPA) together with other estrogenic chemicals, may be responsible for the disrupting effects observed in fish of the middle River Po. The present study has investigated the potential role of BPA in inducing this kind of effects and to this aim, 1-year-old (k1) common carp were exposed for 14 days to graded concentrations of BPA (1, 10, 100, and 1000microg/L). Histological alterations of gonads were described and compared to vitellogenin (VTG) and sex steroid levels. In carp males, BPA caused severe alterations of testis structure starting from 1microg/L. Several specimens lost the typical lobular structure showing spermatogenic cysts intermingled with free spermatozoa often degenerating into the lumen. Oocyte atresia was observed starting from 1micro BPA/L, concerning 57.1% of females at the highest concentration (1000microg BPA/L). A few carp from the same highest treatment also showed intersexuality (27%). Oestradiol-17beta (E2) significantly decreased both in 1 and 10microg BPA/L exposed carp reaching again values not significantly different from control in 1000microg BPA/L. At this concentration, a significant reduction of testosterone (T) was observed in both males and females. The mean plasma concentration of VTG significantly increased in 1000microg BPA/L exposed carp, even if a growing number of responsive carp was observed starting from the environmental concentrations (1 and 10microg BPA/L).