Polyinosinie-polycytidylic acid (Poly I:C) administered intraperitioneally to mice produced an increase in the level of interferon in the tissues of the spleen, liver, lung, and kidney. The level of circulating serum interferon also was increased by the polynucleotide. 2. The highest titer of interferon, presumably resulting from the greatest response to poly I:C was measured in the splenic tissue. 3. Morphine inhibited the poly I:C induced increase in all tissues and circulating serum. The decrease in interferon titer was similar in spleen and serum. 4. These results may indicate the serum level of interferon was more closely related and dependent upon events occuring in the spleen than in the other tissues.
