Pseudomonas fragi, a psychrotroph bacterium involved in meat product spoilage, was shifted either from 5 degrees to 20 degrees C or 30 degrees C and from 28 degrees to 34 degrees C. The heal-shocked cells in the mid-log phase rapidly reached the characteristic growth rate of the postshock temperature. The patterns of synthesized proteins were compared by autoradiography of two-dimensional gel electrophore-grams; The rates of synthesis, after transfer of cells from 5 degrees to 30 degrees C, 5 degrees to 20 degrees C, and 28 degrees to 34 degrees C: changed for 30, 26, and 31 proteins respectively, of which 19, 17, and 12 were increased respectively. Thirteen proteins changed similarly for the three treatments, and two of the seven overexpressed proteins were immunologically related to the Escherichia coli DnaK and GroEL heat shock proteins. From the four low-molecular-mass proteins, belonging to the family of DNA-binding cold shock proteins (CSPs) such as CS7.4, the major E. coli CSP [15], the amounts of C7.0 and C8.0 decreased rapidly after the upshifts, whereas that of E7.0 and E8.0 increased greatly.