Aim of the study was to assess the effectiveness and tolerability of sublingual captopril (SLC) versus sublingual nifedipine (SLN) in treating hypertensive emergencies. During hypertensive crises (systolic blood pressure exceeding 200 mmHg and diastolic blood pressure exceeding 115 mmHg) forty hypertensive patients received either 25 mg of SLC or 10 mg of SLN in a randomized single blind fashion. Blood pressure and heart rate were then controlled after 5, 10, 15, 20, 30, 45, 60, 120 min. and, in 18 cases, up to the 8th hour from the administration. Our results showed: 1) a satisfactory control of the hypertensive crises in 80% of patients treated with SLC with a significant blood pressure reduction after 10 min. (13/8 mmHg, p less than 0.02), while the maximum hypotensive effect was achieved after 30 min. (52/36 mmHg, p less than 0.001); SLN was able to reduce blood pressure in 90% of all the cases, with a significant reduction after 5 min. (15/11 mmHg, p less than 0.02) and hypotensive peak after 20 min (57/38 mmHg, p greater than 0.001); 2) no significant differences for hypotensive effectiveness between the two groups, but with SLC having a mildly delayed onset of action when compared to SLN; 3) antihypertensive effect lasting for about 6 hours in patients treated with SLC and blood pressure progressively raising after 4 hours in patients who received SLN; 4) a significant correlation between blood pressure reduction and blood pressure before drug administration in both groups; a significant correlation between pretreatment PRA and antihypertensive effect in the SLC group. We conclude that both drugs are effective and useful in treating hypertensive emergencies. Anyway we think that in severe forms SLN should be preferred for the shorter time preceding onset of action.