Amongst 40 patients undergoing cardiac transplantation between 1981 and 1984 and treated with cyclosporin A, 23 had hypertension. Fifteen of these patients, aged 39 years (16-57 years), without cardiac failure, treated with 8 +/- 3 mg kg-1 d-1 of cyclosporin A and 0.27 +/- 0.1 mg kg-1 d-1 of prednisolone were studied on average 288 days after transplantation (63-788 days). Blood pressure in the out-patients department of these 15 patients was 164 +/- 14/112 +/- 13 mmHg, in the absence of any antihypertensive treatment for more than 15 days, with a urinary sodium of 104 +/- 48 mEq/d and a urinary potassium of 55 +/- 13 mEq/d (mean +/- standard deviation). Two abnormalities accompany the raised blood pressure: a reduced creatinine clearance of 63 +/- 30 ml min-1 and an increased plasma volume of 445 +/- 686 ml (p less than 0.05) with reference to Hurley's norms (1975). By contrast, urinary excretion of VMA and metanephrines were invariably normal. Plasma renin activity (PRA) was normal in a lying position (1.02 +/- 0.42 ng ml-1 h-1) and after orthostatic stimulation (2.55 +/- 1.31 ng ml-1 h-1). Renin release was not stimulated by acute inhibition of converting enzyme (1.11 +/- 0.70 ng ml-1 h-1). Plasma aldosterone (110 +/- 52 pg ml-1), plasma angiotensinogen (924 +/- 213 ng/ml) and converting enzyme activity (30 +/- 6 mU ml-1) were normal. In these patients with a denervated heart, the orthostatic position increased heart rate from 85 +/- 11 to 93 +/- 12 beats/min.(ABSTRACT TRUNCATED AT 250 WORDS)