The purpose of this study was to analyse the effect of two gas mixtures, containing 40% CO2/30% O2/30% N2 and 45% CO2/5% O2/50% N2, on the microbiological flora (total bacteria count, H2S-producers microorganisms and enterobacteria) and some biochemical indexes (trimethylamine, total volatile basic nitrogen and biogenic amines) of chilled shrimp. Modified atmosphere packaging (MAP) on shrimps delayed the microbial growth compared to air-packed or iced stored shrimp as well as the trimethylamine and total volatile nitrogen production. However, the production of some biogenic amines seemed to be enhanced during the storage of MAP-shrimp.