We studied the elicitation of contact sensitivity to Candida albicans antigen in guinea-pigs with experimental cutaneous candidiasis and in humans, using commercially available potent 1:100 C. albicans antigen (Torii) by patch testing on abraded skin. In guinea-pigs, non-immune animals became patch test-reactive 4-5 days after topical application of viable C. albicans, either under occlusion or without occlusive dressings, concurrently with the demonstrability of delayed responses to intradermally injected 1:10 000 Candida antigen. In humans, all healthy adults who showed delayed hypersensitivity reactions to intradermally injected 1:10 000 C. albicans antigen demonstrated positive patch-test reactions to 1:100 C. albicans antigen. There was a significant correlation between the magnitude of responses to these tests. In contrast, no positive patch test reactions were elicited to the 1:100 C. albicans antigen on neonatal skin, emphasizing the lack of irritability of this test agent. These results also indicate that in humans contact sensitivity to Candida antigen occurs during later life because C. albicans is a ubiquitous organism. The practical value of this Candida patch test for evaluation of patients' immune function was assessed by a prospective study in patients with various skin disorders. The results obtained suggested some potential value of the test for evaluation of cell-mediated immune function of patients with regard to ubiquitous recall antigens.