One-hundred patients suffering from slight-moderate hypertension (53 m, 47 f, aged between 18 and 78, average 49.08) have been studied in order to assess the effectiveness and tolerance of lisinopril ("Zestril", ICI-Pharma), a new ACE inhibitor in a single daily administration at doses of between 10 and 80 mg in relation to pressure values. Monotherapy with Lisinopril proved effective in 84 patients (88.4%), in 74 of whom (7.9%) pressure values were returned to normal. 11 patients (11.6%) did not respond to treatment. In most cases, the result was obtained with a dose of 20 mg in a single administration (32.6%). The incidence of side-effects was limited and in no case required the withdrawal of the drug.