All cases in a population-based series of myeloproliferative and lymphoproliferative (LP) disorders diagnosed in usual residents of Tasmania between 1972 and 1980 were asked for occupational histories and the occurrence of similar diseases in their close relatives. Occupational risks were observed for males who had farmed, mined, or worked in foundries and for women who had farmed or had been hairdressers. For individual diagnoses, the risk to farmers was seen to vary with age at diagnosis, sex, and region. With regard to familial risks, the LP and MP groups seemed to breed true, relatives being affected with a disorder from the other group not more often than would be expected by chance. The risks were of two kinds: Those to siblings and that between parent and child, particularly between mother and son. Occupational risks for the familial cases were limited to farming particularly in males diagnosed at 65 years of age or older. Females possessed elevated risks for the LP group only, and their highest relative risk was for those diagnosed before age 65. This evidence suggests that familial clustering of these disorders partly may be due to common environmental exposures in males from rural kindreds.