Summary:We compared the efficacy and tolerability of isradipine (ISR) and fosinopril (FOS) once-a-day administration in 17 outpatients, 9 men and 8 women, aged 35-65 years (mean + SD = 58 k 10 years), affected by mild to moderate primary systemic hypertension. The patients were given singleblind placebo for 2 weeks and thereafter, in double-blind, randomized, crossover sequence, ISR (5 mg) and FOS (20 mg), both fur 4 weeks. At the end of each period, patients underwent 24-h noninvasive blood pressure (BP) monitoring by means of an A&D TM 2420 Monitor Model 7, with readings taken every 10 min during the day (from 7 A.M. to 11 P.M.), and every 20 min during the night (from 11 P.M. to 7 A.M. were observed in any patient under either therapy. Both ISR and FOS resulted in very effective decrease in BP; however, FOS proved to be significantly more effective than ISR.