The distribution of tet(34) was examined among oxytetracycline (OTC) resistant Vibrio strains isolated from Japan, Korea and the Philippines. tet(34) was detected in 10 isolates (6 in fish, 4 in seawater) from Japan and Korea, suggesting that it is widely distributed among fish and seawater bacteria in these countries. Ninety-eight percent of the Vibrio strains in the Philippines were sensitive to OTC, but none of the 60 isolates from the Philippines. The minimum inhibitory concentration (MIC) of OTC-resistant isolates increased 2 to 8 fold in the presence of Mg²⁺, and MICs were higher in the Japanese and Korean isolates than the Philippine isolates. The MIC for furaltadone (FD) was low in Japanese (23.9%) isolates at over 3.1 μg/ml and high in Korean (50%) and Philippine (56.7%) isolates. This was probably due to the different frequency of use of FD in these countries. Sequences of 16S rDNA of tet(34)-positive isolates were 100% identical, suggesting that tet(34) is conveyed in a particular Vibrio species.