Milks (bovine and human) and dairy products (butter, cheese, skim and whey powders, calf-replacer, casein, butter-oil and dietetic food) were collected during 1971/2 throughout Ireland together with a more limited sample of the 10 major animal feed ingredients, and analysed for organochlorine insecticide residues using electron-capture gas chromatography. The different materials contained low or negligible levels of chlorinated insecticides. Apart from some of the animal feed ingredients the DDT residues were generally the predominant contaminants detected together with lower levels of γ-BHC (lindane), aldrin/dieldrin and heptachlor/heptachlor epoxide. The maximum levels of these insecticides in the bovine milk and dairy products (511, 100, 62 and 21 μg/kg fat respectively) constitute only 50% or less of the Codex Tolerance Limits. The correspondingly low residue levels in the human milk (maxima of 128, 1, 1, and 5 μg/kg fat respectively) which at most represent insecticidal ingestion by infants equivalent to 13, 0·05, 5 and 5% respectively of the WHO/FAO acceptable daily intake for DDT, γ-BHC, aldrin/dieldrin and heptachlor/heptachlor epoxide again pose no obvious health hazards and are strongly indicative of negligible organochlorine contamination in the general diet. The samples of animal feed ingredients examined also contained trace levels of organochlorines (maxima of 0·9, 0·1, 1·6 and 1·0 μg/kg respectively). More extensive monitoring of the residues in animal feed ingredients (the most probable source of milk contamination) is advocated, and the desirability of tolerance limits for insecticides in animal feeds discussed.