Using basal isocratic equipment of HPLC and only one step extraction the determination of urinary free cortisol is available in non specialized laboratory. Results are displayed about reliability and specificity of the method. An extraction coefficient of 97.8 per cent, a good practicability in connection with the use of C18 column chromatography and a reagent flow of 0.5 ml/min. enable a low cost of this determination. Reference values are established for a working adult population.