Serial serum gamma-glutamyl transferase (GGT) levels were estimated in 23 consecutive patients admitted to hospital with a diagnosis of acute stroke. The proportion of patients with elevated GGT levels in the initial, 36-hour and 72-hour samples was 13%, 30% and 24% respectively, suggesting a transient rise following a stroke. Patients with a history of diabetes mellitus had an initial serum GGT level 21 IU/l (95% confidence interval 6 to 37) higher than non-diabetics. We conclude that GGT levels after a stroke may reflect a history of diabetes and cerebral damage as well as the usual more established causes. Physicians, therefore, should be wary of attributing all unexplained high GGT levels in stroke patients to alcohol.