Offspring of female rats injected daily with dl-methadone hydrochloride (5 mg/kg, IP) or saline were cross-fostered at birth to form drug groups exposed throughout gestation only, or both gestation and lactation; controls were exposed only to saline. At approximately 80 days, 120 offspring (20 from each drug group and 60 controls, sexes equally represented) were adapted to a 23-hr water deprivation schedule and individually trained to obtain water in a test cage containing a single water spout. Each methadone-exposed rat then competed with a control animal for access to the water during two 5-min sessions. Under competitive conditions, methadone-exposed rats spent less time at the water spout than did the controls (p less than 0.02); this effect occurred in males and females from all three drug group, and was unrelated to body weight. These results suggest that social dominance may be reduced in the offspring of mother rats given methadone.