Twenty-four-hour blood pressure (BP) monitoring with a noninvasive device (Kontron) has been used to assess the effect of a single dose of indapamide in a group of patients with essential hypertension. Originally 23 patients were selected. Three patients withdrew from the study because of refusal to go through the second 24-hour recording. Eight of the remaining patients had to be excluded for technical reasons, which left 12 patients available for analysis. All patients received a single dose of indapamide, 2.5 mg/day. Before treatment began, a 24-hour BP control was performed, and a second one a month later (37 +/- 8 days). The age of the patients was 46 +/- 10 years. Diurnal BP (8 am to 10 pm) and heart rate were, respectively, 148 +/- 15/101 +/- 6 mmHg and 79 +/- 9 beats/min; night BP (10 pm to 8 am) was 131 +/- 15/88 +/- 7 mmHg and heart rate 71 +/- 10 beats/min. After therapy, diurnal BP was 131 +/- 15/92 +/- 7 mmHg (-15 +/- 7/-8 +/- 4: p less than 0.0001/p less than 0.0001); heart rate 82 +/- 8 beats/min (difference not significant); night BP was 115 +/- 13/80 +/- 8 mmHg (-16 +/- 11/-8 +/- 7: p less than 0.0001/p less than 0.0001) and heart rate 70 +/- 9 beats/min (difference not significant). Twenty-four-hour systolic work values were 106 +/- 15 at the beginning of the trial and 96 +/- 14 (-9.7 +/- 14; p less than 0.05) after 1 month of indapamide treatment. Variability did not change with treatment.(ABSTRACT TRUNCATED AT 250 WORDS)