Between 1976 and 1986, 258 incidents of suspected scombrotoxic fish poisoning were reported in Britain. Histamine analysis was carried out on 240 fish samples from these incidents, and 101 were found to contain greater than 5 mg histamine/100 g fish. The symptoms most consistently reported were rash, diarrhoea, flushing and headache. In recent years there has been a decrease in the number of confirmed scombrotoxic outbreaks and a trend towards more sporadic incidents. Of fish samples with greater than 20 mg histamine/100 g, 94% were from incidents in which scombrotoxic symptoms were characteristic, but where fish had 5-20 mg/100 g only 38% of incidents were clinically distinctive. Guidelines are presented based on the interpretation of quantitative histamine analysis of fish samples from scombrotoxic poisoning incidents.