The possible side effects of particles of polytef paste, a sterile mixture of polytetrafluoroethylene, glycerin, and polysorbate on rapidly growing fetal tissue, were investigated as the first part of a three-stage study designed to investigate the effects on the renal cortex of the periureteric injection of polytef, as used in the treatment of severe vesico-ureteric reflux. Eighteen New Zealandar fetal rabbits were injected with polytef and 8 were injected with normal saline as a control. The group injected with polytef had a 20% maternal death rate, 100% fetal loss and a high rate of fetal growth failure. Postmortem examination of two rabbits that died before delivery, did not reveal any fetal tissue in the uterus, nor did examination of the uterus from 1 surviving rabbit that did not deliver. However, all the fetal rabbits injected with saline had normal birth weights; there was no fetal loss or prematurity. Surgeons using polytef paste should be aware of its effects on rapidly growing fetuses.