Five psychrophilic Antarctic bacteria have been selected for their capacity to secrete exoenzymes into culture medium. These strains are able to grow from 0 to about 25 degrees C. However, production of lipase from Moraxella, alpha-amylase from Alteromonas haloplanctis, beta-lactamase from Psychrobacter immobilis and protease from Bacillus is maximal at temperatures close to that of their environment (-2 to 4 degrees C) and is strongly inhibited at higher temperatures. This thermal effect involves alterations in the secretory pathway in the upper range of temperatures, losses due to the enzyme thermal lability and in some cases to reduction in cell development. The apparent optimal activity temperature of these enzymes is between 30 and 40 degrees C, i.e. about 20 degrees C lower than that of their mesophilic counterparts.