It was proposed that zinc and taurine interact in vivo to influence reproductive outcome in the rat. The effect of taurine deficiency induced by guanidinoethyl sulfonate (GES), a taurine transport antagonist, on fetal development was examined. Female Sprague-Dawley rats were mated overnight and assigned to 1 of 4 treatments through gestation. Animals received taurine-restricted diet and 0.5% 1.0% or 2.0% GES in drinking water. Control animals received taurine-adequate diet and no GES. Taurine deficiency produced a sharp decline in maternal and fetal liver taurine (