The aims of this study were to identify a psychrotrophic bacterium, strain CR41, producing a cold adapted protease during growth at low temperatures and to evaluate the ability of the cells to hydrolyze hake fish protein. The strain was isolated from the intestinal tract of hake collected from the San Jorge Gulf (Patagonia, Argentina) and it was identified as Pseudoalteromonas. Growth and fish protein hydrolysis were determined using an aerated simple mineral medium plus 10% fish protein concentrate. Proteolytic activity was measured at 7 and 22 degrees C during culture in the concentrate. Protease production started in the exponential growth phase and reached a maximum during stationary phase. Protease activity at 7 degrees C was lower than at 22 degrees C. After 8 h of incubation, the percentage of hydrolyzed protein was 84% at 7 degrees C and 95% at 22 degrees C. Electrophoresis detection showed that degradation of muscle hake proteins was complete at both temperatures, and in gelatin zymograms extracellular activity showed two proteolytic bands with apparent molecular masses of approximately 31.6 and 62 kDa.