Six lactating women undergoing contrast media examination had milk and blood taken to determine the rate and extent of excretion of iohexol (Omnipaque) (four mothers) and metrizoate (Isopaque) (two mothers). Blood samples were taken up to 45 minutes and milk samples up to 48 hours after the contrast medium injection. The excretion was low, reaching a maximum at 3 to 6 hours and showing a slow decay curve (t1/2 = 15 to 108 hours). One mother, who was weaning her baby, showed a different excretion pattern. The amount excreted during 24 hours was about 0.5 per cent of the weight adjusted maternal dose for both iohexol and metrizoate. It is not likely, that such a low dose of poorly absorbed drug would cause any adverse effects in the infant, unless it is hypersensitive to the drug already. The authors consider breast feeding to be acceptable for mothers receiving iohexol or metrizoate.