10 healthy young subjects drank, on three separate occasions, the equivalent of three gin and tonics containing 50 g alcohol and 60 g sucrose, gin and "Slimline" tonic containing 50 g alcohol and 0.5 g sucrose, or tonic alone containing 60 g sucrose. Their behaviour, symptoms, blood-glucose, and plasma-insulin were monitored for 5 hours. Both of the alcohol-containing drinks caused mild-to-moderate inebriation, but gin and slimline tonic had no significant effect on either blood-glucose or plasma-insulin levels. Gin and tonic provoked a greater insulinaemia and more profound reactive hypoglycaemic response than tonic alone, and in 3 of the subjects this was associated with the appearance of neuroglycopenic symptoms. Alcohol-mediated reactive hypoglycaemia may contribute significantly to motor-car accidents in the late afternoon at a time when blood-alcohol levels have fallen below the legal limit.