The long-term efficacy of isradipine, a new dihydropyridine calcium antagonist with marked vascular selectivity, was evaluated in 17 patients with essential hypertension. All had a supine diastolic blood pressure of greater than 95 mmHg with 10 mg pindolol once daily. After a short-term, double-blind, dose-finding, crossover comparison with addition of isradipine or placebo twice daily, they continued on pindolol and their optimal dose of isradipine in a single-blind, long-term follow-up study. Eighteen patients were recruited but one male patient discontinued treatment after 2 weeks due to ankle oedema and will not be accounted for in the overall evaluation. There were 11 males and six females with a mean age of 56 +/- 10 years. In the short-term study on the optimal dose of isradipine (5.1 mg twice daily) blood pressure was lowered by 24/18 mmHg (P less than 0.001). No change in heart rate was seen despite the substantial drop in blood pressure. In the long-term study the patients were seen for a mean follow-up time of 12.5 months (range 4-17 months). After the longest follow-up time mean arterial pressure was 107.0 +/- 7.4 compared with 120.1 +/- 8.2 mmHg after placebo baseline [delta = 13 mmHg (11%), P less than 0.001, n = 17]. The heart rate was unchanged (delta = 0.2 beats/min, 95% confidence limits -3, +3), and so was ankle circumference (delta = 0.12 cm, 95% confidence interval, -1, +1). On the other hand, mean weight was reduced by 2 kg from 90 kg (P less than 0.05, n = 17).(ABSTRACT TRUNCATED AT 250 WORDS)