In vivo historical control data, including mortality, body weight, food and water consumption, and clinical signs in F344/DuCrj rats were obtained from 11 long-term toxicity and carcinogenicity studies conducted at the Biosafety Research Center, Foods, Drugs and Pesticides, (An-Pyo Center) during the last five years. Survival at 109 weeks of age was 80.2% (min: 74%, max: 90%) in males and 80.5% (min: 72%, max: 92%) in females. The maximum mean body weights of males and females were 443.3 +/- 15.8 g (mean +/- S. D.) and 295.7 +/- 13.3 g respectively. Male rats attained their maximum body weight at 82.6 +/- 5.3 weeks of age, the females at 103.5 +/- 2.5 weeks of age. Clinical symptoms increased with age, particularly after 84 weeks of age, and included: wasting, piloerection, palpable subcutaneous and abdominal masses, and decreased spontaneous movement. Lowered body temperature and auricular pallor occurred commonly in moribund animals. The nature and grade of toxicity in the treated animals were generally disclosed by comparing with the behavior and signs in the control animals. The use of in-house, historical control data can be useful in subsequent evaluations of chronic toxicity and carcinogenicity studies.