Exposure histories in acute nonlymphocytic leukemia patients with a prior preleukemic condition. A subset of patients with acute nonlymphocytic leukemia (ANLL) have evidence of a myelodysplastic syndrome (MDS), low infiltrate leukemia, or other preleukemic condition that may be present for several months before onset of disease. The hypothesis that these conditions act as markers for environmentally induced cancer was examined in 270 ANLL patients, 46 with a preleukemic phase and 224 with an acute onset. Although the effects of previously identified risk factors (male sex, age older than 50 years, prior cytotoxic therapy) were demonstrated, no associations with common environmental conditions (cigarette smoking, alcohol use, occupations with exposure to chemicals or radiation) were present with the exception of hobbies involving potential chemical exposure, odds ratio (OR) and 95% confidence intervals = 4.2 (1.4 to 12.3) and self-reported exposure to pesticides, OR = 10.2 (1.8 to 63.1). These may be chance associations although a previous case-control study of MDS reported similar findings. 