Different strains of Vibrio parahaemolyticus (Vp) in broth cultures and Vp-inoculated live Pacific oysters (Crassostrea gigas) were subjected to high pressure processing (HPP) at 241, 276, 310, and 345 MPa. Results showed Vp numbers were reduced by HPP in both pure culture and whole oysters. Vp inactivation was dependent on time and pressure. Optimum conditions for reducing Vp in pure culture and oysters to non-detectable levels were achieved at 345 MPa for 30 and 90 s, respectively. Resistance variations were detected between Vp in pure culture and in oysters. HPP proved to be an efficient means of reducing Vp in oysters. The decimal reduction rates of Vp 03:K6 strain was compared with clinical ATCC 17802 and environmental AST Vp strains in pure culture and Pacific oysters under high pressure processing (HPP) at 276 and 310 MPa for different treatment times based on Calik and others (2001) data. Results showed that 03:K6 strain had relatively higher decimal reduction rates when compared to two other strains. The 03:K6 strain in oyster had the highest D-value of 1.77 min under 276 MPa HPP treatment. Reduction trends presented by Vp 03:K6 strain must be considered when making commercial HPP setting decisions for reduction of Vp. / Graduation date: 2002