We have investigated the structural requirements for vitamin A suppression of interferon production and inhibition of interferon action. Inhibition of interferon action seems to be most dependent on the side chain of the vitamin A molecule. The side chain apparently requires a conjugated double bond system and a hy-drophilic terminal group to inhibit interferon action. In contrast, the ring portion of the vitamin A molecule seems to be most important for the suppression of interferon production. © 1976, SAGE Publications. All rights reserved.