Upon mixing detergent solutions with the neutral fluorescent molecule 1,6-diphenyl-1,3,5-hexatriene a large increase in fluorescence is observed if detergent exceeds the critical micelle concentration. This property has been used to determine the critical micelle concentration of anionic, uncharged, zwitterionic, and cationic detergents. Regardless of detergent charge, the critical micelle concentrations obtained agree with the values obtained by other methods. This fluorescence assay is both sensitive and rapid, and should provide a simple and general method for determination of critical micelle concentration of any detergent.