As a preliminary to the study of desoxyribonuclease elaboration by resting cells, 34 strains of streptococci were examined for their capacity to produce desoxyribonuclease in broth cultures. The largest amounts of enzyme were found to be produced by strains belonging to Lancefield group A and by certain strains belonging to groups C and D. Many strains, especially those belonging to other groups, produced little or no enzyme. Washed cocci of certain strains elaborated desoxyribonuclease extracellularly upon suspending them in a solution containing an energy source, phosphate and magnesium ions. When any one of these factors was omitted, no enzyme was produced. The appearance of extracellular desoxyribonuclease was found to be inhibited by a variety of enzyme poisons, and this and other findings indicate that desoxyribonuclease is synthesized in the resting cell system. Cocci were found to contain a substance which partially inhibits the desoxyribonuclease formed by group A strains but which fails to inhibit the desoxyribonuclease formed by strains belonging to groups B and C or to inhibit the desoxyribonuclease derived from yeast, barley, and pancreas. The inhibitor of group A desoxyribonuclease has been identified as streptococcal ribonucleic acid. Preparations of ribonucleic acid derived from yeast differed from streptococcal ribonucleic acid in failing to inhibit the group A desoxyribonuclease.