A study of 250 patients with pathologically confirmed testicular cancer diagnosed between January 1977 and June 1980 and 250 population controls matched for age and residence was carried out to investigate risk factors for testicular cancer. This paper reports results of risk associated with occupational exposure to extreme (< or = 60 degrees F or > or = 80 degrees F), high (> or = 80 degrees F), and low (< or = 60 degrees F) temperature. Interviews of approximately 1.5 h duration were conducted by trained male interviewers, using a standardized interview schedule. Mantel-Haenszel methods and logistic regression models were employed to estimate these temperature effects on risk of testicular cancer. The estimated adjusted odds ratios of testicular cancer, when 16 potential confounders were controlled for, were 1.71 (95% Cl: 1.13-2.60) for occupational exposure to extreme temperatures; 1.70 (1.04-2.78) for low temperature; and 1.20 (0.80-1.80) for high temperature. The findings suggest that occupational exposure to extreme, low, and high temperature may increase risk of testicular cancer, independent of other potential risk factors.