Chronic rejection is the most important cause of renal graft dysfunction. Non-immunological mechanisms have been suggested as a probable origin of chronic graft rejection, provoking a decrease in renal mass function, followed by glomerular hyperfiltration in the remnant nephrons, which could cause progressive glomerulosclerosis and functional loss. Early, or preclinical, identification of patients with glomerular hyperfiltration, defined as an increase in glomerular filtration fraction (GFF) and in glomerular capillary pressure (GCP), could prolong graft life. The objective of this study was to evaluate, non-invasively, stable renal graft haemodynamia and early glomerular hyperfiltration. We studied 116 renal transplant patients with stable renal function and five healthy living kidney donors with normal renal function. Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were determined using 51Cr-EDTA and o-[131I]iodohippurate, respectively. GFF was obtained from the relation between GFR and ERPF, and GCP from a mathematical model (Hall-Gomez' formula). A simultaneous analysis of renal function was performed. In transplant patients, the GFR and ERPF were significantly lower than in healthy, living, kidney donors (P<0.02). The same trend was observed for GCP (P<0.01), while GFF was not significantly different. Twelve patients (10.3%) had criteria of glomerular hyperfiltration. In patients without criteria of glomerular hyperfiltration, plasma level and clearance of creatinine were 128+/-33 micromol.l-1 and 56+/-15 ml.min-1, respectively; and in those patients with glomerular hyperfiltration criteria were 108+/-18 micromol.l-1 (P=NS) and 83+/-24 ml.min-1 (P=0.002) respectively. It is concluded that determinations of GFR, ERPF, GFF and GCP allow non-invasive evaluation of renal graft haemodynamia and can be useful in the early detection of glomerular hyperfiltration.