Abstract: The cuprammonium reagent of Grimble et al. (Ibid., 1983, 128, 422) was modified so that final concentration. of active constituents in the reaction mixture were: 1.0 mM Cu(II), 0.4 M NH3 and 0.2 M NaOH (in excess); the absorbance (at 280 nm) of the modified reagent blank was <50% of that of previous methods. The new reagent was most sensitive for the colorimetric determination of polyols, especially D-glucitol, but it also produced a better color yield for some aldoses and disaccharides than the original reagent. It was used for post-column HPLC detection of various sugars and polyols; calibration graphs for D-glucitol, D-mannitol and D-glucose were rectilinear from 40 to 180 nmol, 0 to 150 nmol and 0 to 300 nmol, respectively. The method was applied in analysis of fungal mycelia.