This report describes the effect of administration of repeated doses of ipodate (Oragrafin; 3 g orally every third day for five doses) in six hyperthyroid patients. Baseline serum concentrations of immunoassayable T3, rT3, and T4, were 926 +/- 206 ng/100 ml, 165 +/- 31 ng/100 ml and 21 +/- 2.7 micrograms/100 ml (mean +/- SEM), respectively. Within 24 h after the first dose of ipodate, serum T3 fell by 54% and it remained between 66-77% below baseline until the third day after the fifth dose; subsequently, there was a gradual recovery from the effect of ipodate. Serum T4 also decreased after ipodate administration; it was 23-31% lower than baseline from the second day after the third dose to the sixth day after the fifth dose. Serum rT3 increased after each dose of ipodate; peak values of 97%-203% above baseline value were observed at 24-48 h after each dose. There was a subjective improvement in clinical symptoms of hyperthyroidism in all cases. Resting pulse rate and pulse pressure dropped significantly (P less than 0.02) by the ninth day of study and remained so thereafter. Body weight increased significantly by the ninth day of the study. The various data suggest that ipodate may serve as a useful adjunct in the early treatment of hyperthyroidism.