The risk of leukemia among farmers and dairy farmers in particular was studied with the use of mortality records from Wisconsin, 1968-76. A comparison of occupation as noted on the death certificate for 1,499 cases and a like number of matched controls revealed a slight [odds ratio (OR) = 1.10], but statistically nonsignificant, excess risk of leukemia among farmers. The risk was highest among those born after 1897 (OR approximately 1.50) or dying before age 71 years (OR approximately 1.35) among dairy farmers (whether noted on death certificates or identified by county agricultural agents of the Cooperative Extension Programs of the University of Wisconsin) and all farmers alike. The under-representation of farmers among controls with smoking-related causes of death, however, may partially account for these findings. Stratification by county of residence showed significantly elevated risks among farmers from counties with heavy dairy production (OR = 1.40) and fertilizer use (OR = 1.42).