Bisphenol-A (BP-A; 4,4'-isopropylidenediphenol) is a monomer of plastics commonly used in various consumer products, and is used as an intermediate in the manufacture of epoxy, polycarbonate, and polyester-styrene resins. A National Toxicology Program carcinogenesis bioassay of BP-A (>98% pure) was conducted by feeding diets containing 0, 1000, or 2000 ppm BP-A to groups of 50 male and 50 female Fischer (F)344 rats; 0, 1000, or 5000 ppm to groups of 50 male B6C3F1 mice; and 0, 5000, or 10,000 ppm to groups of 50 female B6C3F1 mice for 103 weeks. The mean body weights of the low- and high-dose rats and of female mice and high-dose male mice were lower than those of the controls throughout much of the study. Lower body weight gains in rats were likely caused by reduced food consumption. Survivals were comparable among groups. Regarding neoplasia, leukemias occurred at increased incidences in BP-A-dosed rats of both sexes: male, 13/50 controls vs 12/50 low-dose and 23/50 high-dose (P < 0.03); in females, the respective findings were 7/50, 13/50, and 12/50. Interstitial-cell tumors of the testes were increased in BP-A-dosed male rats: 35/49 controls vs 48/50 (P < 0.01) and 46/49 (P < 0.01); and an increasing trend was observed for mammary gland fibroadenomas in male rats (P < 0.05, 0/50 controls vs 0/50 and 4/50). In male mice, lymphomas/leukemias were increased: 2/49 controls vs 9/50 (P < 0.05) and 5/50. Multinucleated giant hepatocytes were observed in male mice (1/49 controls vs 41/49 and 41/50), whereas there was no increase of liver tumors. In their BP-A bioassay report, the National Toxicology Program concluded that there was no convincing evidence that BP-A was carcinogenic for rats or mice. However, the marginal increases in leukemias in male and female rats, along with increases in the combined incidence of lymphomas and leukemias in male mice, suggest that BP-A may be associated with increased cancers of the hematopoietic system. Increases in interstitial-cell tumors of the testes in rats were also evidence of carcinogenesis, as was the unusual occurrence of mammary gland fibroadenomas in male rats.