Abstract:The performances of eight healthy young males were tested 1–3 hrs after oral administration of placebo, 10 mg diazepam (mean serum levels 286–281 ng/ml respectively), ethanol (mean serum levels 0.080–0.043), or the same amount of ethanol (mean serum levels 0.081–0.045) combined with 10 mg diazepam (mean serum levels 289–339 ng/ml). Both ethanol and diazepam reduced concentration, efficiency, and attention (Osgood Test). Combined administration augmented this subjective impression, and also reduced motivation. Ethanol significantly (α = 0.05) reduced the score in the Minor Tracing Test, and diazepam significantly reduced the score in the Letter Cancellation, Flicker Fusion Frequency, and Mirror Tracing tests, and in the Clinical Examination. Combined administration of ethanol and diazepam increased the detrimental effects on the tests mentioned above, and also increased the effect on Time Evaluation Ability (not significant) and Complex Coordination (α = 0.04) and Sorting tests (α = 0.055). Generally diazepam slowed the subjects, ethanol speeded them up, but increased their errors, combined administration both slowed them up, and increased