Plasma total, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol concentrations were determined in 32 patients admitted with either acute nonlymphocytic leukemia or chronic myelogenous leukemia in blast crisis. Measurements were repeated in 15 of these individuals during a leukopenic period induced by chemotherapy and in 6 of the latter group when they had achieved remission. Initial plasma total, LDL, and HDL cholesterol levels in 15 male (111.9 +/- 27.9; 53.7 +/- 10.4; 23.7 +/- 22.5 mg/dl) and 17 female (124.0 +/- 42.0; 68.6 +/- 32.0; 29.4 +/- 13.9 mg/dl) patients were markedly reduced compared with age and sex-matched control values (all P less than 0.01). Remission in six subjects was associated with significant increases in total cholesterol (162.0 +/- 61.0 vs. 111.5 +/- 47.9 mg/dl; P less than 0.02) and LDL cholesterol (106.8 +/- 51.2 vs. 43.5 +/- 31.3 mg/dl; P less than 0.05) compared with their baseline values. Chemotherapy-induced leukopenia was associated with inconsistant changes in plasma cholesterol levels although LDL cholesterol increased in all patients who subsequently achieved remission. LDL cholesterol levels fell dramatically in two patients who relapsed. These results indicate that LDL cholesterol concentrations may be of value in assessing disease activity in individuals with acute myelogenous leukemia.