Caveolae are plasma membrane invaginations that contain a variety of signal transduction molecules and receptors for growth factors and cytokines. This study was performed to examine the in vivo expression and localization of caveolin-1 in kidneys from 19 children who underwent surgery release of ureteropelvic junction obstruction (UPJO) in relation to renal function and degree of tubulointerstitial fibrosis. Renal biopsies were carried out at the time of surgery for obstruction release. Kidney tissue from children of similar age removed because of carcinoma was used as control. Expression of caveolin-1 at the protein level in renal tissue and urine was demonstrated in patients with technetium 99 m labeled diethylene triamine pentaacetate (99Tc DTPA) renal scan 28.8±2% and increased tubular interstitial fibrosis in seven patients at the time of obstruction release. Colocalization staining of AT1 angiotensin II receptor with caveolin-1 in basolateral membrane of epithelial tubule cells, enhanced AT1 messenger ribonucleic acid (mRNA) and decreased endothelial nitric oxide synthase (eNOS), were shown in these patients. In contrast, absence of association of caveolin-1 with AT1 receptor expression in proximal and collecting tubule membranes with AT1 receptor mRNA and eNOS mRNA expression near control were demonstrated in 12 patients, with 99Tc DTPA renal scan 39.7+2.1% and no evidence of tubulointerstitial fibrosis. From our results, the role of caveolin-1 as a factor contributing to the severity of the tubulointerstitial process resulting from obstructive nephropathy could be suggested.