Technetium-99m diaminocyclohexane (DACH) is a new tubular agent excreted via a cationic transport mechanism, like cyclosporine-A (CsA), It is expected that Tc-99m-DACH will permit effective assessment of tubular function in CsA-treated patients. To establish the pharmacokinetic characteristics of Tc-99m-DACH and to ascertain whether this new agent is useful in CsA-treated patients, 11 healthy volunteers and 15 CsA-treated patients underwent renal imaging and clearance studies using Tc-99m-DACH and chromium-51 ethylene diamine tetra-acetic acid (EDTA). 99mTc-DACH yielded satisfactory dynamic renal images in all participants. The mean plasma clearance of Tc-99m-DACH was significantly greater than that of Cr-51-EDTA In volunteers (109.4+/-19.7 ml/min versus 86.6+/-13.7 ml/min, P<0.05). However, the urinary excretion of 99mTc-DACH at 90 min was significantly lower than that of Cr-51-EDTA (46.1%+/-9.3% versus 53.1%+/-8.6%, P<0.05), most probably due to its partial parenchymal retention. The elimination half-life of Tc-99m-DACH was significantly increased in CsA-treated patients in comparison to volunteers, and consequently the plasma clearance values were significantly suppressed in these patients, in contrast to Cr-51-EDTA and endogenous creatinine clearance values. In conclusion, our findings indicate that Tc-99m-DACH, as a sensitive marker of cationic tubular function, could be used to monitor renal haemodynamics in patients receiving CsA treatment.