An investigation comprising 49 environmental (VAE), 7 human isolates (VAH) and 3 type culture (VAT) strains of Vibrio alginolyticus showed a very high similarity among the strains. By primary isolation a swarming activity on blood agar and a yellow, hemispheric relatively large colony type on TCBS were very conspicuous. Besides the characteristics of Vibrionaceae the most typical and differential diagnostic important features were: sucrose fermentation, lysine decarboxylase activity, acetoine and 2,3 butanediol production, no growth on an electrolyte deficient medium (CLED), arginine and arabinose negative reaction. Swarming on blood agar and growth in 10% NaCl were also important although one of these criteria might be negative. An obvious difference was observed in ornithine where the percentage of positive VAE, VAH and VAT were 51, 100 and 0, respectively. In cellobiose all VAE and VAT but only two VAH were positive. MR positive strains were also found among all categories. The G + C mol% in the strains ranged from 45.9 - 46.8.