In vitro lymphocyte proliferation in response to phytohemagglutinin and streptokinase-streptodornase and delayed dermal hypersensitivity to several antigens were assessed in patients with mild viral upper respiratory infections. The response to phytohemagglutinin in 18 patients was not diminished during the viral infection. Deoxyribonucleic acid synthesis induced by streptokinase-streptodornase...