Abstract: Gas-Liquid chromatographic assay of D-mannose in serum hydrolysates by utilizing aldononitrile acetate derivatives for the diagnosis of deep candidiasis are reported. 20 patients with both systemic and disseminated candidiasis as well as controls were examined. We found mannose level was the highest in disseminated candidiasis (925.24±73.64μg/ml), lower in systemic cases (654.58±31.19 μg/ml) and was much lower in healthy adults (502.76±76.83 μg/ml) (P<0.01).The concentration of serum mannose increases rapidly from 267.36 to 1053.57 μg/ml one day after inoculation of Candida albicans in experimental rabbits. While it was negative in specimens of Cryptococcus neoformans, Aspergillus fumigatus, Fonsecaea pedrosoi and some common strains of bacteria. This method is valuable for the diagnosis of both systemic and disseminated candidiasis particularly in the early stage of the latter.