A monthly survey on the distribution of human-pathogenic Vibrionaceae of the seawater from five principal harbors in Taiwan was conducted by National Quarantine Service from July, 1991 to February, 1994. Of the total 1,167 Vibrionaceae isolates, strains of Vibrio alginolyticus (449 strains) were the most frequently isolated, followed by Vibrio parahaemolyticus (262) , Aeromonas hydrophila (153), Vibrio cholerae non-O1 (86), and Vibrio vulnificus (67). None of Vibrio cholerae O1 was isolated. The pH, salinity, and water temperature in this study ranged from 5.8 to 8.6, 0.1 to 4.2% , and 15 to 34 degrees C, respectively. It is concluded that the family Vibrionaceae exists autochthonously around the coastal waters in Taiwan.