Death certificate analyses of white California [USA] males aged 20-64 yr dying from 1959-1961 indicated unusually high mortality rates in farm laborers from respiratory diseases and accidents. To determine whether this mortality pattern was pervasive among agriculturally employed workers, similar analyses in Iowa from 1971-1978 were completed. Only mortality from work-related accidents was excessive; respiratory disease deaths were no more frequent than among the general population. The reason for high respiratory disease mortality in California remains unknown. The 2 worker populations differed with respect to ethnic background, socioeconomic status, mobility and accessibility of medical care. Worker exposures to agricultural chemicals and to dust were substantial in both regions but were qualitatively different. One or more of these factors could account for the different rates of respiratory disease mortality.