The Cockcroft-Gault formula enables a rapid prediction of the creatinine clearance (CCr) to be made without having to collect urine and using the variables of plasma creatinine, body weight, sex and age. The formula was used to predict the CCr in 100 consecutive patients and comparisons made with the measured CCr and the 51chromium EDTA clearance. The advantages of being able to quickly predict the creatinine clearance using this formula are discussed.