Recall of delayed type hypersensitivity (DTH) as a test for cell-mediated immune competence was assessed in 254 subjects using the Multitest device which delivers seven skin-test antigens intradermally; 77 subjects were tested concurrently by Multitest and a conventional panel of six antigens. Similar results were obtained with Multitest and the conventional panel (R = 0.65). Reproducibility of Multitest between three observers, who independently assessed the aggregate size of reactions (the reaction score) in 45 subjects, was high (R = 0.89). Twenty-four subjects were tested twice 3 months apart; the correlation for the reaction score was high (R = 0.88), demonstrating the suitability of Multitest for serial studies of immune function. Anergy was infrequent (1%) among 110 healthy male controls but was more frequent (8%) among a group of 101 healthy male homosexuals (P less than 0.05). The response rate to particular test antigens differed for the three Australian groups tested and a previously studied French group. Hence there is a need to establish normal profiles of DTH responsiveness for different geographic areas, as well as among subjects of known age and sex, when assessing cell-mediated immunity by the level of DTH responsiveness to multiple skin test antigens.