The effects of diazepam (DZ) infusions on changes in adrenocorticotropin hormone (ACTH) are a source of debate. In this study, 66 healthy young adult men were evaluated for changes in plasma ACTH after intravenous infusions with placebo, 0.12 mg/kg and 0.20 mg/kg of DZ. After the higher DZ dose, 85% of the subjects demonstrated a decrease in ACTH of 20% or more, with the nadir occurring between 30 and 60 min postinfusion and values returning to baseline levels by 180 min. These results support the conclusion that at the clinically relevant doses used here, DZ infusions are associated with a significant decrease in ACTH.