Ethanol administered to animals is known to cause hypocalcemia. This investigation was undertaken to evaluate direct early effects of ethanol on the net fluxes of Ca2+ and inorganic phosphate (Pi) into or out of bone using tibiae from 13-day-old chick embryos and 8-day-old suckling rats in vitro. When chick bones were incubated with ethanol in the medium (10 microliters/ml), net Ca2+ efflux was decreased 19, 22, 27, and 31% at 2, 4, 6, and 8 h, respectively. Metabolically inhibited bones showed a net influx rather than efflux of Ca2+ and were not further affected by ethanol. The ethanol had no consistent effect on net Pi efflux and slightly reduced lactate production. At three doses of ethanol (3, 10, and 30 microliters/ml of medium) the reduction of Ca2+ efflux was dose related in both chick and rat bones. Ethanol completely inhibited parathyroid hormone-stimulated, net Ca2+ efflux from chick bones, even at ethanol levels that by themselves did not affect Ca2+ efflux. These findings are consistent with the hypothesis that the hypocalcemia in ethanol-treated animals may be due in part to inhibition of net Ca2+ efflux from bone.