The adverse effect of diving on the fetus may extend beyond n gestational process and outcome. Primiparous Sprague-Dawley rats were assigned to one of ten exposure schedules during gestatred PO2 level, the following question about the effect of exposing a pregnant female to high partial pressure of inspired oxygen has been raised. "What effect does an increased maternal PIO2 have on fetal arterial PO2 and therefore on possible fetal oxygen poisoning?" This study was carried out to observe the effects of maternal hyperoxia on gestational process and outcome. Primiparous Sprague-Dawley rats were assigned to one of ten exposure schedules during gestation. The treatment groups were subjected to either the high concentration of oxygen, or the high atmospheric pressure. On day 21 of gestation, laparotomy was performed to examine for number and distribution of implantations and live and resorbing embryos. Fetuses were weighed, and examined for gross malformations. Subsequently, they were fixed, measured in physical parameters, and examined for visceral anomalies. Minor visceral anomalies and anatomical variation was not found. Similarily, there were no significant differences when number of resorptions, mean fetal weights, pregnancy interruption rate were compared by analysis of variance. These results indicate that exposing rats to oxygen at increased atmospheric pressure doese not affect fetal health or survival.