Prolactin release in response to suckling was examined in primiparous lactating rats two hours after alcohol administration. Litters were adjusted to eight pups on lactation day 2 and dams were implanted with an atrial catheter on day 6. On day 10, pups were separated from the mother at 0800 h. An extension was attached to the catheter at 1100 h. Following removal of a baseline blood sample an hour later, rats were infused with alcohol doses of 0, 0.5, 1.0, 2.0 or 2.5 g/kg body weight. Two hours later, pups were returned to dams. Subsequent blood samples were obtained 10, 30, 60, 120 and 180 min after the onset of suckling. Following 10 min of suckling, plasma prolactin for groups of rats infused with alcohol at 2.0 and 2.5 g/kg body weight were lower than control, 0.5 and 1.0 g/kg groups. The blood alcohol level (BAL) for the 2.0 g/kg group was 94 +/- 8 mg% and for the 2.5 g/kg group was 162 +/- 4 mg%. After 30 min, the BAL for the 2.5 g/kg group was 134 +/- 5 mg% and plasma prolactin was suppressed in this group compared to control, 0.5 and 1.0 g/kg groups. The BAL for the 2.0 g/kg group after 30 min of suckling was 74 +/- 9 mg% but prolactin was not significantly lower than controls. We conclude that in rats, alcohol inhibition of suckling-induced prolactin release is directly correlated to the BAL. The threshold BAL which effectively inhibits this prolactin release is lower than the human legal intoxication level.