The plasma concentration profile of disopyramide was examined in 13 patients with arrhythmias following acute myocardial infarction. Intravenous loading doses of 1.5 mg/kg followed by 0.7 mg/kg and then infusion of 0.3 mg kg-1h-1 resulted in final concentrations between 2.4 and 4.9 mg l. Change-over to oral therapy with disopyramide sustained release (SR) tablets was smooth, and therapeutic plasma concentrations were maintained throughout. Comparison of the plasma concentrations in a subsequent cross-over study with disopyramide plain capsules 150 mg every 6 h and SR tablets 250 mg every 12 h, each being administered for 3 days to attain a steady state, showed that the bioavailability and the variation of the plasma concentration were similar with both regimens. In patients with body weight between 62 and 92 kg disopyramide SR tablets 250 mg every 12 h matched the preceding infusion rate of 0.3 mg kg-1h-1 resulting in plasma concentrations close to steady state already on the first day of oral therapy. The absorption of disopyramide SR tablets is only moderately delayed, and the preparation can be used twice daily in direct succession of intravenous infusion.