BACKGROUND: V. parahaemolyticus, an important seafood-borne pathogen, is the causative agent of gastroenteritis in humans. In this study, the occurrence and distribution of the thermostable hemolysin (tdh) gene and the tdh-related hemolysin (trh) gene were investigated, and as many as 72 different O:K serovar combinations were determined from diarrheal patients and environmental sources in Gyeongbuk provinceas during the 2000-2001. METHODS: A total of 50 strains of V. parahaemolyticus isolated from diarrheal patients and environmental sources were analyzed for the tdh gene and trh gene. The strains were analyzed for kanagawa phenomenon (KP) with the wagatsuma blood agar medium test. Furthermore, the strains belonging to O and K serotypes were determined. DNA sequence determination of the tdh gene were verified using GenBank and analyzed. RESULTS: In the KP experiments of V. parahaemolyticus, 80% of the strains isolated from diarrheal patients showed positive, but all of the strains isolated from environment sources were negative The distribution of O and K serotypes were O3:K29, O3:K6, and O3:K31, atc. isolated from diarrheal patients, and O2:K28, O3:K29, and 04:K34 atc. isolated from environmental sources. As for the tdh and trh gene of V. parahaemolyticus, the tdh gene was detected from 88.0% of diarrheal patients and 16.0% of environmental sources. The trh gene was not detected from diarrheal patients and 8.0 % of environmental sources, whereas all urease positive strains possessed the trh gene. The DNA sequence of tdh gene were verified using GenBank and analyzed the difference, tdh nucleotide sequence was found among the V. parahaemolyticus. CONCLUSION: V. parahaemolyticus is distributed with high frequency in the environmental sources such as sea water, fishes and shellfishes sampled at the Gyeongbuk coastal area, and the O3:K6 strains producing TDH were confirmed, which is prevalent throughout the world, from diarrheal patients. Thus, it is very important to establish a measure to prevent food poisoning by V. parahaemolyticus.