Metabolic profiles of urine extracts of humans with viral infections, as well as of media of virus-infected human tissue cultures, have been analyzed by non-fragmenting mass spectrometry and compared with corresponding controls. The spectra were then subjected to several alternative computerized statistical procedures to detect diagnostic biochemical profiles. Controlled longitudinal studies on fully informed, consenting volunteers who received sandfly fever virus demonstrate the onset of a characteristic metabolic pattern that precedes the onset of symptoms and subsides when the patients overcome the infection. Longitudinal studies of human tissue cultures infected with poliomyelitis virus demonstrate characteristic metabolic patterns within a few hours after infection. Non-fragmenting mass spectrometry may thus provide the clinical laboratory with a sensitive, reliable test for viral infections significantly faster than attainable by current techniques.