Levels of I were determined in selected foods and dietary supplements, and in samples of the British ‘Total Diet’. The average concentration of I in British milk collected in thirteen areas on four occasions during 1990 and 1991 was 150 μg/kg (range 40–310 μg/kg), compared with 230 μg/kg in 1977–79. No difference was found between skimmed and whole milk. Winter milk contained 210 μg/kg while summer milk contained 90 μg/kg. Regional differences were less pronounced than seasonal differences. Levels in fish and fish products were between 110 and 3280 μg/kg. Edible seaweed contained I levels of between 4300 and 2660000 μg/kg. Kelp-based dietary supplements contained I at levels that would result in a median intake of 1000 μg if the manufacturers' recommended maximum daily dose of the supplement was taken, while other I-containing supplements contained a median level of 104 μg in the manufacturers' maximum recommended daily dose. Intake of I, as estimated from the Total Diet Study, was 173 μg/d in 1985 (277 μg if samples with very high I contents were included) and 166 μg/d in 1991. These levels are above the UK reference nutrient intake of 140 μg/d for adults but well below the Joint Expert Committee on Food Additives provisional maximum tolerable intake of 1000 μg/d.