This range-finding study was conducted for M & T Chemicals, Inc. to establish dose levels for a teratogenicity study in rats with Tributy1tin Oxide. The test material was administered by gastric intubation to mated female rats (5/group) from Days 6-19 of gestation at dose levels of 2, 6, 18 and 54 mg/kg. Included in the study was a vehicle (corn oil) control group (5 females). Females were sacrificed on Day 20 of gestation, uterine implantation data were recorded, fetuses weighed and given a gross external examination. At dose levels of 2 and 6 mg/kg none of the females died and no obvious treatment-related effects on maternal body weight data, uterine implantation data and fetal body weight data were evident. Likewise, external examination of fetuses recovered from these females were unremarkable. At the 18 ag/kg dose level, one female died during the dosing period. A reduction in mean body weight on Day 20 of gestation was noted and mean weight gain during the Day 6-20 gestation interval was also lower than control. In-life observations revealed several females in poor condition with a yellow- staining in the ano-genital region and clear nasal discharge on Days 10 and 15 of gestation. Uterine implantation data were similar to control but mean fetal weights were lower than control. External examination of the fetuses recovered at this dose level were unremarkable. At the 54 mg/kg dose level, none of the females survived to Day 2C sacrifice.