Twenty healthy male volunteers completed an open, partially randomised, crossover study to assess a possible pharmacokinetic interaction between nisoldipine and quinidine. Volunteers received either 1 nisoldipine coat-core 20mg tablet once daily, or 2 quinidine gluconate 324mg tablets twice daily, according to a randomised 2-period crossover design. Between the 2 treatment periods there was a washout phase of 7 days. After a further washout phase of 7 days, all volunteers received nisoldipine coat-core 20mg (1 tablet) and quinidine gluconate 648mg (2 tablets) concomitantly, as well as a second quinidine gluconate 648mg (2 tablets) dose 12 hours later. The results of this study indicate that the concomitant administration of nisoldipine and quinidine has no effect on the bioavailability of quinidine. However, it cannot be ruled out that the concomitant administration of these 2 drugs has an attenuating effect on the bioavailability of nisoldipine, although the clinical significance of a possible attenuation may be small in view of the very high intrasubject variation of this parameter. Concomitant administration of nisoldipine and quinidine was well tolerated.