In order to evaluate the mid-term effects of amlodipine, a 1,4-dihydropyridine calcium antagonist, as well as its effects on the renin-angiotensin-aldosterone system (RAAS), on water and electrolyte balance, on urinary excretion of albumin (UAE) and on lipid metabolism, thirteen hypertensive patients (2 M, 11 F, mean age 54 years) were studied in the course of 24 weeks of therapy with amlodipine at 5-10 mg/day. Pre-therapy and periodically during therapy, the systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) were recorded in the sitting orthostatic positions (2 measurements). Laboratory tests were performed at times O and at 24 wks with the patients fasting for at least 12 h in the recumbent position. The tests included: plasma renin activity (PRA), plasma aldosterone (PA), serum angiotensin converting enzyme (SACE), blood urea nitrogen (BUN), blood creatinine, plasma electrolytes (Na, K, Cl), triglycerides, total cholesterol (TC) and HDL-cholesterol (HDLC), along with 24-h urine samples (with sterile urine) to determine UAE. The results of this study demonstrate that SBP, DBP and HR were significantly reduced during the 24 wks of therapy. The water and electrolyte and renal function were not modified. After treatment the levels of TC were significantly reduced. No change was observed in the RAAS, while the mean levels of UAE were reduced though not significantly. In conclusion, amlodipine was shown to be effective for the therapy of hypertension; it does not cause reflex tachycardia even in mid-term therapy and was effective in reducing TC levels.