A culture of Pseudomonas fluorescens was isolated which had definite psychrophhilic attributes and a very active enzyme constitution. This culture was found to produce heat labile endo-and extracellular proteolytic enzymes. The extracellular proteinases were recovered by ammonium sulfate precipitation. Extracellular proteolytic enzyme elaboration was shown to be inversely proportional to the tempreature at which the culture was grown, at least from 0 to 30C. The extracellular proteolytic enzymes were found to be more active per unit weight than the endocellular enzymes. Temperatures above room temperature were demonstrated to have adverse effecrts on cell production and endocellular proteolytic activity. Increases in temperature greatly accelerated the action of proteolytic enzymes of this culture once they were elaborated. On the basis of pH optima and other criteria, several different endo-and extracellular enzymes were produced by this culture of P. fluorescens.