A histological analysis of 200 male eelpout gonads was performed as part of biological field studies carried out in coastal waters of Denmark during prespawning and spawning time in May-June. In the marine environment, the eelpout is often selected as sentinel species. Histology of the testis revealed the presence of intersexuality in specimens from all six areas investigated with a prevalence ranging from 8 to 36 % of the male population (on average 22 %). The intersex condition was defined by the simultaneous presence of primary oocytes within apparently normally developing testis tissue. The severity of histological alterations ranged from a single oocyte to several hundreds in a pair of testes cross sections. In severe cases, the primary oocytes and oogonia could be either clustered or evenly distributed in the tissue. Presence of secondary oocytes was not detected in any sample. The eelpout exhibited the highest intersex prevalence at contaminated marine stations, but also occurred at sites with apparently little pollution. Severity of abnormality was not proportional to prevalence. The findings suggest that feminized male fish were exposed to endocrine disrupting substances in their environment early in life. Concurrent reference sampling of male and female eelpout in different development stages evidenced also female specimens with a high proportion of atresia in the ovaries.