A cohort mortality study was undertaken of forestry workers at a public electrical utility who had worked for six months or more during 1950-82 and who were routinely exposed to herbicides including phenoxy acids. A total of 1222 men with 25 274 years at risk experienced 80 deaths. Ascertainment of vital state at the end of follow up was 95.5%. The male population of the province (Ontario) was used as the reference group. Overall, no excess mortality was found in this cohort relative to the reference population. A statistically significant increase in deaths occurred, however, due to suicide (SMR = 210, 95% confidence interval, 95% CI 105-376) for the cohort as a whole. No deaths were seen due to cancers such as soft tissue sarcoma and non-Hodgkin's lymphoma that have been cited by other authors as being associated with exposure to phenoxy acid herbicides. Although the cohort is not large, the absence of deaths due to these cancers is consistent with findings from other studies with sufficient numbers to allow examination of specific risks. The cohort is still young, however, and at the end of follow up most had not reached an age when increased incidence of cancer would normally be expected.