The distribution of renin was investigated by immunofluorescence in human kidney biopsy specimens (27 patients with lipoid nephrosis, 39 with Berger disease, 17 with membranous glomerulonephritis, 5 with thrombotic microangiopathy, and 7 with malignant nephroangiosclerosis). A semiquantitative assessment was carried out. Two ratios were found significatively increased in the study groups as compared with the control group: JGA + and JGA ++ which expressed, respectively, the number of fluorescent JGA in relation to the number of glomerular sections and the number of fluorescent JGA with more than six renin-containing cells (RCC) in relation to the number of immunoreactive JGA. Highest values were observed in patients with thrombotic microangiopathy and malignant nephroangiosclerosis (P less than 0.001). The above immunomorphological parameters were correlated with clinical and laboratory data. A positive dependency was found between JGA + and JGA ++ ratios and a low sodium diet, diuretic therapy and serum creatinine. A negative dependency was seen in the albumin and hemoglobin serum levels. No correlation was found with blood pressure values. These observations suggested that decreased plasma volume and impaired renal function could be factors leading to an increased renin production in the kidney.