In an open study, thirteen chronic dialysis patients with nonvolume dependent uncontrolled hypertension were treated with pinacidil for a mean period of 43 weeks. Seven patients were taking concomitant antihypertensive therapy. Twelve patients achieved long-term blood pressure control on a mean dose of 33 mg/day. The baseline supine blood pressure was 184/116 mmHg. After 1 week it had fallen to 161/95 mmHg and blood pressure control was maintained over the study period. Patient weight remained stable. The baseline reading was 61.6 kg and at the end of the study it was 59.7 kg. Pulse rate did not change significantly. For the eight patients not taking beta-blockers the mean change in pulse rate was 7.6 beats/min supine and 6.3 beats/min erect (NS). Pretrial urea and creatinine were 27.6 mmol/l and 1027 mumol/l and after 25 weeks they were 29.6 mmol/l and 1087 mumol/l, respectively (NS). Four patients had ECG evidence of left ventricular hypertrophy before the study and one on completion of the trial. Five patients showed correction of T-waves on their ECG's. Six patients experienced side effects, none of which warranted withdrawal of treatment. These findings suggest that pinacidil is a valuable alternative treatment for hypertensive dialysis patients.