The present study was conducted to develop a special formula to predict creatinine clearance (CCr, ml/min) in the elderly with chronic muscle atrophy using serum albumin (Alb, g/dl). We obtained 90 data sets including actual body weight (BW, kg), urinary creatinine excretion (UCr, mg/24 h), serum creatinine (SCr, mg/dl), and Alb from 90 inpatients aged 60-92 years. Regression equations were determined between the dependent variable of UCr/BW and the explanatory variable of Alb as follows: For males Ucr/BW = 2.695 Alb + 4.665 For females Ucr/BW = 1.827 Alb + 4.146. Then, the new predictive formula was derived from the equations: For males CCr = (19Alb + 32)BW/(100 x SCr) For females CCr = (13Alb + 29)BW/(100 x SCr). Evaluations for the predictive error (predicted CCr- measured CCr) showed that the new formula could provide more accurate and less biased estimates of CCr than the Cockcroft and Gault formula could, even in patients with renal insufficiency and in those with Alb < or = 2.8 g/dl.