Previous analysis of Iowa death certificates from 1971 through 1978 identified several cancers with significantly elevated mortality in farmers. Subsequent ecological studies identified farm practices, including pesticide usage, that might be associated with these mortalities. These results led to several case-control studies and a similar analysis of more recent death certificates. 'Usual occupation' has been added to the death certificate tapes for the years 1979-1986. Cancer mortality in Iowa farmers for this period is very similar to that for 1971-1978. Case-control studies for acute lymphocytic leukemia and multiple myeloma indicated that farming in general is not a risk factor for either cancer type. However, exposure to general classes of insecticides and herbicides is associated with an elevated odds ratio in farmers for incidence of multiple myeloma. The odds ratios are not statistically significant at the 5% level, probably due to relatively small numbers of cases and controls exposed to any one class of pesticides.