Neoplastic data on 1370 control Wistar rats from 10 carcinogenicity bioassays done between 1980 and 1990 were reviewed. Mean percentage survival at 104 weeks was 58% for males and 59% for females. A total of 1857 neoplasms were diagnosed in 466 (68%) male and 582 (85%) female rats; 1390 were benign and 467 were malignant (12% with metastasis). Seventy-four percent of all neoplasms were in endocrine and reproductive systems. Most common neoplasms (affecting more than 7% of either sex) were pituitary adenoma (27.7% males; 55.0% females), mammary fibroadenoma (1.0% males; 25.3% females), mammary adenocarcinoma (1.0% males; 13.1% females), adrenal cortical adenoma (8.3% males; 9.3% females), and endometrial stromal polyp (9.6% females). Fourteen neoplasms affecting 2 to 6% of either sex included adrenal pheochromocytoma, thyroid C cell adenoma, thyroid follicular adenoma, pancreatic islet cell adenoma, lymphoma, histiocytic sarcoma, thymoma, hepatic adenoma, pancreatic acinar adenoma, mammary adenoma, dermal fibroma, astrocytoma, testicular interstitial cell tumor, and ovarian granulosa cell tumor. Remaining neoplasms were seen in less than 2% of animals.