The in vitro activity of a naturally occurring complex carbohydrate, CAN-296, was evaluated by testing 132 clinical and ATCC isolates of yeast and Aspergillus fumigatus, many of which were azoic-resistant. The in vitro susceptibility tests were performed by standardized broth microand macrodilution methods and results were compared with those obtained for amphotericin B, fluconazole, ketoconazole, flucytosine and the pneumocandin L-733, 560. All tested Candida species showed highly uniform susceptibility to CAN-296 at concentrations of 0.078 to 0.312μg/ml; non-albicans Candida were as susceptible to CAN-296 as the Candida albicans strains. Multi-azoleresistant Candida species were highly sensitive to CAN-296. Minimum inhibitory concentration measurements did not differ from minimum lethal concentrations by more than two-fold for all tested Candida species. Aspergillus fumigatus, on the other hand, showed only moderate susceptibility to CAN-296. The kinetics of the anti-Candida activity of CAN-296 was investigated by killcurve experiments using C. albicans and C. glabrata and the results were compared with those obtain for amphotericin B. CAN-296 was found to be rapidly fungicidal in concentrations ranging from 4°C fold the mean MIC value. The broad spectrum of anti-Candida activity together with the rapid fungicidal effect make this complex carbohydrate a promising agent for clinical use.