During the last decade the iodine supply in Germany has increased significantly, but there is still a high frequency of goitre. Therefore the question of iodine bioavailability has arisen. In a two-period study 12 women were given a mixed diet of ordinary foods with milk and milk products of different batches. None of the volunteers suffered from an iodine deficiency according to WHO-criteria. Each period ended with a 9-day balance-study protocol in which all foods were provided. Food and fluid intake were registered, and urine and faeces were quantitatively collected. The iodine content was determined by ICP-MS. The mean intake in the form of solid food amounted to 175 +/- 10 micrograms I/d and to 27 +/- 15 micrograms I/d in fluid form. Milk and dairy products represented the main source of iodine (37%). Iodine was predominantly excreted in the urine (89%, 171 +/- 45 micrograms I/d) and the faeces 11% (20 +/- 11 micrograms I/d). The resulting iodine balance was approximately . In one case an iodine-rich erythrosine preparation with a low iodine bioavailability was used. Between the two periods of consuming different batches of milk and milk products no differences were observed concerning the high bioavailability of iodine.