In an attempt to improve therapeutic decision-making in severe hypertension, different blood pressures (BP) were correlated with target organ damage in a cross-sectional study of 20 asymptomatic patients. Casual BP was 197/117 (s.d. 31/10) mmHg despite therapy. Each subject was assigned an end-organ score on the basis of the number of silent cerebrovascular damages detected by magnetic resonance imaging, funduscopic retinopathy, cardiac hypertrophy by echocardiography, and renal involvement evaluated by isotopic renography. The pooled scores for target organ damage showed significant correlations with an elevated asleep mean ambulatory (amb-) brachial systolic (r = 0.84) and diastolic BP (r = 0.88) but not with either awake amb-BP (means or peak values), causal BP or invasive radial BP at the clinic. Night-time amb-DBP increased with age in contrast to the daytime DBPs. Furthermore, the nocturnal fall in mean arterial amb-BP was significantly less in patients aged > or = 60 years, average 5%, than in patients < 60 years, 16%. This may have prognostic implications even if, after age adjustment, the inverse relation (r = -0.78) between the end-organ scores and the dip in BP did not reach independent significance. The close association of cardiovascular complications with night-time rather than daytime BP emphasises the importance of making a prospective study in this field, trying to optimise the nocturnal BP in severe hypertension.