Measurement of blood (1→3)-β-D-glucan is useful for early diagnosis and follow-up of the therapeutic process of deep seated mycoses. The Fungitec G test MK (Seikagaku Corp., Tokyo) kit usingalkaline-pretreatment followed by chromogenic kinetic assay has been widely used in Japan becauseof its high sensitivity and easy handling of a large number of samples. Discrepancy in the levels of (1→3)-β-D-glucan and/or in the quantitative judgement, however, has been pointed out between this kit and other commercial kits. One of the reasons for this discrepancy has been reported to be nonpecific reactions caused by substances other than β-glucan.In this study, we have improved the alkaline pretreatment reagent by changing the concentration of KOH and salts, resulting in a marked reduction of the non-specific reaction. Recovery of standard β-glucan added to plasma or serum after the improved pretreatment was 80 to 120%, and no amidolytic activity was detected either in plasmaor in serum. By the improved pretreatment, the incidence of non-specific reactions, i.e., those that ex-ceed the quantitation limit (3.9 pg/mL), were markedly decreased from 139 to 16 out of 200 plasmasamples and from 106 to 22 out of 170 serum samples. The incidence of strong non-specific reactions, i.e., those that exceed the cut-off level (20pg/mL), were also decreased from seven to one with plasma and seven to zero with serum samples. Correlation between corrected β-glucan measurements by the current pretreatment and non-corrected ones by the improved pretreatment was quite good.The improved method is thus expected to decrease the frequency of non-specific false-positive reac-tions, with the high sensitivity of Fungitec G test MK.