1. Glomerular angiotensin II (ANG II) binding has been studied in normotensive (NTR) and spontaneously hypertensive (SHR) rats at 5, 10, 15 and 20 weeks of age. 2. Binding of 125I-labelled ANG II by glomeruli from NTR and SHR was similar at 5 and 10 weeks of age, with 5 week values of 426.4 (range 384-469) and 400.2 +/- 245 fmol/mg of protein; however, at 15 and 20 weeks ANG II binding by SHR glomeruli was significantly greater than by NTR, with 20 week values of 614.7 +/- 245 and 308.3 +/- 31.8 fmol/mg of protein, respectively (P less than 0.01). 3. The ANG II binding affinity constant (Ka) of glomeruli from NTR and SHR was comparable at 5, 10 and 15 weeks of age, with values of 1.5 (range 1.1-1.9) and 1.08 +/- 0.35 nmol/l, respectively, at 5 weeks; whereas at 20 weeks the Ka for SHR glomeruli was significantly greater than for NTR, with values of 1.85 +/- 0.45 and 0.66 +/- 0.22 nmol/l, respectively (P less than 0.001). 4. Age-related changes in glomerular binding of ANG II in SHR were not found to be related to changes in either plasma renin activity or systolic blood pressure.