Interleukin-4 (IL-4) has been recently implicated in the pathogenesis of glomerulonephritis. However, the expression of IL-4 and IL-4 receptor (IL-4R) in human kidney has not been fully determined. Nonradioactive in situ hybridization was used to examine the expression of IL-4 mRNA and IL-4R mRNA in tissues from normal kidneys and specimens from a variety of human kidney diseases. In normal glomeruli, a few mesangial cells and cells of the Bowman's capsule weakly expressed IL-4 and IL-4R mRNA, whereas in diseased glomeruli both mRNA types were strongly expressed in resident glomerular cells, including mesangial cells, glomerular epithelial cells, and cells of the Bowman's capsule. The relationship between the expression of these mRNA and the degree of glomerular injury was different in different types of glomerulonephritis. In IgA nephropathy and non-IgA mesangial proliferative glomerulonephritis, IL-4 expression correlated positively with the degree of mesangial hypercellularity and extracellular matrix expansion. However, IL-4R expression was relatively constant. In contrast, the expression of IL-4 and IL-4R mRNA correlated negatively with the degree of glomerular injury in lupus nephritis. Coexpression and discordant expression of these mRNA forms were observed in individual cells. In tubulointerstitium with severe lesions, IL-4 mRNA and IL-4R mRNA were observed in atrophic tubules and some of the infiltrating cells and fibroblasts. The interstitial expression of these mRNA forms was similar in IgA nephropathy, non-IGA mesangial proliferative glomerulonephritis, and lupus nephritis and correlated positively with the degree of tubulo-interstitial changes. These results suggest that an autocrine and/or paracrine pathway of IL-4 is present in human diseased kidneys and that IL-4 may be involved in tissue injury in glomerulonephritis.