The cell-mediated immunity of patients who had basal cell carcinomas (BCCs) removed was studied by measuring cuntaneous delayed hypersensitivity reactions to recall antigens (Multitest CMI, Pasteur-Merieux), and by measuring lymphocyte counts and subsets. One group of patients had multiple BCCs (3 or more) removed and were considered to have a high risk of new BCC formation. The other group consisted of patients who had one BCC and had not developed another within 5 years; these were considered to have a low risk of new BCC formation. The low-risk patients had significantly larger cutaneous reactions to recall antigens (p < 0.05) and significantly fewer were anergic (p < 0.01). There was a correlation between smaller cutaneous reactions and increasing numbers of BCCs (p < 0.05). There was no significant difference between the groups in lymphocyte counts or subsets, but the low-risk patients had a significantly higher CD4:CD8 ratio (p < 0.05) than the high-risk group. The Multitest CMI test can be used to determine which patients are at risk of developing many BCCs.