BACKGROUND The cause of hyperalbuminuria in hypertonic patients can be functional or irreversible structural changes. The objective of the present investigation was an attempt to differentiate these two possibilities by comparing data of hypertonic patients with normal albuminuria (albumin excretion < 20 micrograms/min) and those with microalbuminuria in patients with renovascular hypertension by comparing findings after successful percutaneous transluminal angioplasty of the renal arteries (n = 8). RESULTS The authors examined 20 patients with normal albuminuria (12 men and 8 women, mean age 46 years) and 20 patients with microalbuminuria (12 men and 8 women, mean age 49 years). Of these patients 8 were examined repeatedly after angioplasty. The examination was made in the morning, renal haemodynamics were assessed by the infusion technique (clearance of polyfructosan and paraaminohippuric acid), in blood and urine the albumin and IgG concentration (bromcresol purpur-Lachema Brno and immunoturbidometrically-Tina-quant Boheringer Mannheim). In hypertonic patients with microalbuminuria a significantly higher (p < 0.001) IgG excretion was found (14.1 as compared with 5.12 micrograms/min.) and a reduced ratio of IgG clearance to albumin clearance (p < 0.001), 0.73 as compared with 1.60. After successful angioplasty of the renal arteries there was a significant drop of the blood pressure (p < 0.05) and of the renal vascular resistance as well as a significant decrease of albuminuria (p < 0.05) on average from 137 to 48 micrograms/min. The quantitative improvement of albuminuria, however, did not go beyond the discrimination value for microalbuminuria. CONCLUSIONS The results suggest that microalbuminuria in hypertensive patients is as a rule a manifestation of structural renal changes, while also functional and reversible changes participate. The asset of treatment of hypertension by angioplasty of the renal arteries was manifested not only in the renal haemodynamics but also by reduced albuminuria.