This study was undertaken to investigate the dynamics of glomerular filtration and serum beta 2-microglobulin in patients with confirmed autosomal dominant polycystic kidney disease (ADPKD) without chronic renal failure (CRF). Twenty five patients (11 women and 14 men, age range 15 to 56 years) with echographically and computer-tomographically proven ADPKD were entered into the study. Glomerular filtration was followed using the 24 hour creatinine clearance and beta 2-microglobulin serum level was measured radioimmunologically using an ABBOTT laboratories kit. 12 patients had a significantly reduced glomerular filtration: 1.01 +/- 0.05 ml/s compared with 2.12 +/- 0.15 ml/l in the control group (P < 0.001). This group of patients also had a significantly increased level of the serum beta 2-microglobulin: 3.54 +/- 0.47 micrograms/l versus 1.42 +/- 0.28 micrograms/l in healthy controls (P < 0.001). Seven of the patients showed normal glomerular filtration and significantly increased beta 2-microglobulin: 2.65 +/- 0.46 micrograms/l (P < 0.05). The glomerular filtration in six of the patients was found to be significantly increased (hyperfiltration) 2.65 +/- 0.04 ml/s (P < 0.001) while their serum beta 2-microglobulin level tended to rise (2.25 +/- 0.3 micrograms/l). We believe that glomerular hyperfiltration combined with the increased level of the serum beta 2-microglobulin can be used as an early marker of ADPKD.