A pharmacokinetic study of ranitidine was performed in 14 patients with haematemesis divided into two groups according to the severity of blood loss. Pharmacokinetic values were calculated from plasma concentrations after the first of three daily injections (100 mg) and compared with those obtained in five healthy volunteers (50 mg i.v.). There were no significant differences between patients in the two haemorrhage groups and controls. The low, or even questionable, effectiveness of histamine H2-receptor antagonists in the treatment of upper gastrointestinal haemorrhage does not seem to be due to pharmacokinetic factors.