Age-adjusted and age-specific incidence rates of testicular cancer in US Navy personnel did not differ significantly from those of the US population, and age-adjusted incidence rates did not increase with length of service in the Navy. There was a group of three occupations, however, which involved duties similar to those of the civilian occupation of automobile mechanic, and which had a significantly elevated age-adjusted rate of testicular cancer compared with the US population and the total Navy population. These occupations were aviation support equipment technician, engineman, and construction mechanic. All involve maintenance of internal combustion engines and exposure to the attendant lubricants, solvents, paints, and exhausts.