Structures of 17 minor forms of aureobasidins (Abs), Abs B~R, were elucidated by mass fragmentation and amino acid analysis. The fragmentation patterns by FAB-MS spectroscopy of Abs A~E seemed to follow predictable rules, so we used the rules to elucidate the 13 other Abs. All Abs consisted of eight amino acids and one hydroxy acid. A new antifungal antibiotic, aureobasidin (Ab) A (Fig. 1), has been isolated from the fermentation broth of Aureobasidium pullulans R106. This strain also produces many antifungal antibiotics with structures that might be related to Ab A. We isolated 17 of these antibiotics and named them Abs B~R. The structures of Abs B~E were elucidated by chemical degradation. Acid hydrolysis of Abs B~E gave amino acids and hydroxy acids. These amino acids were analyzed by HPLC or NMR. The structures of the hydroxy acids were confirmed by comparison with synthetic compounds. Alkaline hydrolysis of Abs B~E gave linear chain peptides. The fragmentation patterns of their derivatives by FAB-MS were used to deduce the amino acid sequences, from which the structures of Abs B~E were identified. We found that the fragmentation patterns by FAB-MS of Abs A~E seemed to follow predictable rules, so we applied the rules to elucidate the structure of the other Abs. The structures of Abs A~R are shown in Fig. 1.