The possible testicular effects resulting from occupational exposure to para-tertiary butyl benzoic acid (p-TBBA) were studied in 90 male volunteers employed at the Martinez, California, facility of the Shell Chemical Company. The comparison data used were obtained from an external reference group of 103 male volunteers not exposed to any known testicular toxin. Exposure indices were based on the calendar years of employment in a given job category. Outcome variables included sperm count, history of fathering children, and gonadotropin levels. It was concluded that p-TBBA, at the levels of exposure experienced at this plant, does not have an apparent clinical or epidemiologic effect on testicular function.