A teratology study was conducted on the fungicide RH-53,866 (Technical),alpha- butyl-alpha-4-chlorop henyl-1H-1,2,4-triazole- 1-propanenitrile, (Lot No. LSPL0017/E, TD No. 83-087, 84.5% active ingredient). The test material was administered orally in corn oil to 25 presumed-pregnant Sprague-Dawley rats (Cr1:CD(SD)BR) in each of 5 groups. Doses of 0.0 (vehicle control), 31.3, 93.8, 312.6, and 468.9 ag/kg/day active ingredient were administered on Day 6 through 15 of gestation. Dose volume was 10 ml/kg and the vehicle control group received only corn oil. Rats were approximately 85 days old when bred and were observed daily for signs of ill health or reaction to treatment. Maternal body weights were recorded on Day 0, 6, 10, 13, 16, 18. and 20 of gestation. Dams were killed on Day 20 of gestation and the number of corpora lutea,resorption sites, and live or dead fetuses were recorded. Live fetuses from each litter were weighed, sexed, and examined for external malformations and variations then prepared for either soft tissue examinations (1/3) or skeleton examinations (2/3). The Fertility Index (No. pregnant/No. presumed-pregnant) was 0.84 or greater in all groups and 0.90 overall. RH-S3,866 caused no deaths at any dose. Clinical signsof toxicity were not observed at 31.3 or 93.8 mg/kg. At 312.6 and 468.9 mg/kg compound-related signs included rough hair coat, desquamation, andsalivation. At 468.9 mg/kg additional signs of reduced fecal output, redexudate from the mouth, and red exudate from the vagina were recorded. Necropsy observations on females at all doses were not remarkable. Maternal body weight during gestation was significantly depressed at 468.9 mg/kg only on Day 10 of gestation and returned to control levels by Day 13.