A fluorimetric method for the determination of plasma cortisol has been studied in detail. The method is based upon reaction with ethanol-sulphuric acid reagent and measurement of the produced fluorescence at exc. 470 and em. 550 nm. Some modifications were suggested regarding extraction solvent and time of the reaction. Under the proposed conditions, the method is rapid and a sensitivity of 1.5 μg/100 ml was attained. It was applied on 29 patients with chronic renal failure and 12 normal subjects. Cortisol levels at 8 AM in patients on either haemodialysis (27.05 ± 8.94 μg/100 ml) or under conservative treatment (45.13 ± 10.68 μg/100 ml) were significantly higher (P < 0.001) than control group (16.12 ± 3.45 μg/100 ml).