A 25-year-old male patient presented with unexplained infertility. Semen analysis showed azoospermia or severe oligoasthenoteratospermia with elevated serum FSH. The history revealed that he had been employed in a chemical factory for 5 years working with chloralkali-electrophoresis. Mercury concentrations in hair, blood, and urine samples were considerably above levels of unexposed controls. Bilateral testicular biopsies revealed marked interstitial lymphatic infiltration. About 33% of the tubules analyzed showed a Sertoli-cell-only (SCO) syndrome and tubular atrophy. Fewer than 4% of tubules showed qualitatively intact spermatogenesis. Autometallographic (AMG) analysis of the biopsy material yielded silver-enhanced mercury grains, primarily in the interstitial Leydig cells. Sections from a control patient not exposed to mercury were devoid of mercury grains.