Summary Sodium molybdate was fed to two Holstein male calves. In general, the usual symptoms of molybdenum poisoning consisting of mild diarrhea, decreased body weight gains, anemia and greying of the black hair areas were observed. In addition, lameness and joint involvement were found. The most striking and heretofore unnoted symptom was the lack of sexual interest or libido exhibited by these two animals. Ilistological examination of the testes showed marked damage to interstitial cells and germinal epithelium with little or no sperma-togenesis present. Further investigations of these effects and the possibility of using molybdenum as a tool in experiments involving the testes and its products are indicated.