We studied the effects of nifedipine on blood pressure and on clinical and analytical parameters in hypertensive patients. Seven male and eight female subjects (mean age of 46.27 +/- 5.38 years, range of 41-56 years) with essential arterial hypertension were given nifedipine (20 mg b.i.d.) for 3 months. Before and after treatment, history, blood pressure, and biochemical values were recorded [blood: Na, K, Ca, creatinine, uric acid, triglycerides, cholesterol, HDL cholesterol, antidiuretic hormone (ADH), and aldosterone; urine: Na, K, Ca, creatinine, ADH, aldosterone, and percentage fraction of Na, K, and Ca excreted]. After 3 months of treatment, we found (a) significant decreases in systolic (147 +/- 18 vs. 166 +/- 16 mm Hg, p less than 0.001) and diastolic blood pressure (90 +/- 8 vs. 107 +/- 8 mm Hg, p less than 0.0007), triglycerides (107 +/- 47 vs. 120 +/- 49 mg/dl, p less than 0.0007), and cholesterol (236 +/- 4 vs. 257 +/- 44 mg/dl, p less than 0.00075) in blood, and in K excretion (50 +/- 19 vs. 46 +/- 19 mEq/g of creatinine, p less than 0.0007) and excreted fraction of K (49 +/- 6% vs. 8 +/- 5%, p less than 0.0012) in urine; (b) significant increases in HDL cholesterol (65 +/- 13 vs. 58 +/- 13 mg/dl, p less than 0.001) in blood, and in Na (115 +/- 73 vs. 109 +/- 69 mEq/g of creatinine, p less than 0.0007) in urine; and (c) no significant change in the remaining biochemical parameters, or in heart rate. Secondary effects included flushing (34%), headache (20%), ankle swelling (17%), dizziness (13%), palpitations (4%), and pruritus (4%).(ABSTRACT TRUNCATED AT 250 WORDS)