AbstractThe interferon mechanism offers the hope for moderate to high level prophylactic immunity of broad antiviral spectrum but of relatively short duration. Economic and biological considerations offer little hope for utilization of exogenous interferon as a prophylactic or therapeutic substance, unless but a small part of the total molecule be found to carry the activity. The real promise for interferon application is in the administration of suitable inducers so as to cause the body to produce and distribute its own interferon. Certain ribonucleic acids (RNA's) offer hope for high level potency as inducers without adverse effect. The condition for interferon induction by ribonucleic acids appears to be double‐ or multistrandedness and freedom from inhibitors. These can be of biologic or synthetic origin. The mechanism of action of interferon is not fully understood but appears to fit into the Jacob‐Monod model involving two phases: first, a derepression by the inducer to cause the cell to form interferon and second, a derepression by interferon to cause recipient cells to form the active substance which acts by preventing translation from viral messenger RNA. Double or multistranded RNA of viral or other origin appears to be unique to the cell and serves as the alert to it to produce interferon in phase 1. Greatest need for interferon is clearly for those diseases in which there is a multiplicity of immunologic types in excess of the numbers which could be put into a vaccine as, e.g., the common cold and enteric viruses. There might be some overall therapeutic benefit also if inducer were given early enough in infection. Special value for interferon induction might derive by administration in early life before the development of immunologic maturity, as a means for preventing infection with oncogenic or other viruses. Additionally, suitable inducers might be capable of interrupting the reinfection cycle in virus‐dependent malignancies.The favorable outlook for interferon utilization must always be tempered with the realization that under certain as yet undiscovered situations, adverse rather than beneficial effects might result from indution of interferon. It is not impossible that in certain special circumstances, as in ordinary immunologic responses, it might be more beneficial to negate rather than to promote the effect.