All drugs should be given with caution to pregnant or breast feeding women. Recent concern about the role of salicylates in the aetiology of Reye's syndrome has prompted the DHSS to restrict the use of aspirin in children. The case of a 9 week old breast fed infant whose serum contained 0.47 mmol/l of salicylate is reported. Her mother was taking aspirin 2.4 g/day, and it is concluded that salicylates must not be taken by breast feeding mothers.