In 84 patients with insufficiently treated essential hypertension (systolic blood pressure > or = 160 mmHg and/or diastolic blood pressure > or = 100 mmHg) and normal renal function (creatinine clearance Mean +/- SD = 114 +/- 22 ml/min/1.73 m2) the mean urinary albumin excretion was 39 +/- 19 mg/24h in comparison to 14 +/- 13 mg/24h (p < 0.001) in 10 healthy controls. In 39 of the hypertensive patients albumin excretion was increased (> 30 mg/24h urine) in a subclinical range (microalbuminuria). After 3 days of effective antihypertensive treatment (systolic blood pressure < 150 mmHg and diastolic blood pressure < 90 mmHg) the mean albumin excretion of the microalbuminuric patients decreased from 66 +/- 33 mg/24h to 44 +/- 28 mg/24h (p < 0.01). 27 of these hypertensive patients showed persistent microalbuminuria; in the other 12 patients with primary microalbuminuria the albumin excretion rate was normal now. In the patients with persistent microalbuminuria the prevalence of hypertensive retinopathy was 85% in comparison to only 33% in the patients with reversible microalbuminuria under intensified antihypertensive treatment (p < 0.01) and 31% in the patients with primary normoalbuminuria. The prevalence of coronary heart disease was 11% in the patients with normoalbuminuria and 29% in those with irreversible microalbuminuria (ns). Thus hypertensive patients with persistent but not with reversible microalbuminuria under short intensive antihypertensive therapy show a statistically significant higher prevalence of hypertensive retinopathy and therefore can be considered as an indicator of general microvascular damage in essential hypertension.