The aim of this study was to determine whether absolute 24 h DMSA uptake measurements (%DMSA) correlate well with 51Cr-EDTA clearance measurements in patients with severely reduced kidney function (SRKF). Between 1990 and 1997, 55 of 482 patients who underwent EDTA clearance measurements also underwent %DMSA within 1 week. Of these, 31 were women and 24 were men (mean age 60 years; range 19-77 years). EDTA clearance was determined using the slope-intercept method. Absolute depth- and background-corrected %DMSA were determined 24 h following the injection of 185 MBq per 1.73 m2 freshly prepared 99Tcm-DMSA. All patients had EDTA clearance < or = 60 ml.min-1. Eighteen patients (group A: 9 men and 9 women, mean age 55.8 years, range 28-73 years) had EDTA clearance > 20 ml.min-1 (mean +/- S.D. = 30.9 +/- 13.8 ml.min-1), whereas 37 patients (group B: 22 women and 15 men, mean age 62.0 years, range 19-77 years) had EDTA clearance < 20 ml.min-1 (mean +/- S.D. = 10.2 +/- 6.6 ml.min-1). EDTA clearance correlated well with %DMSA for the patients as a whole and for group A (r = 0.87, P = 0.73; r = 0.79, P = 0.0001 respectively). The regression equation suggests that %DMSA is not a marker of early renal dysfunction. In group B, the r-value (r = 0.48, P = 0.004) suggests that %DMSA is reliable as a marker of severe renal dysfunction to the extent that it provides rough information. In conclusion, %DMSA may not be used as a marker of early renal impairment. Additionally, in patients with severely reduced kidney function (EDTA clearance < 20 ml.min-1), it only provides a rough estimate.