Eleven patients with influenzalike illnesses were skin tested with tuberculin, histoplasmin, coccidioidin, trichophytin, and candida antigens during the acute phase of their illness and again one month later. Seven patients had serologically proven influenza and four had noninfluenzal febrile respiratory diseases. Only the group with influenza manifested significant hyporeactivity to the skin-test antigens during illness. Despite the decrease in skin reactivity during influenza, phytohemagglutinin stimulated the lymphocytes of the four patients who were studied during both the acute and convalescent phases. No decrease in skin-test reactivity was observed after immunization against influenza in four patients.