The cellular response to Leishmania major was evaluated in vitro with a lymphocyte proliferation microtest, performed on 100 microliters of whole blood obtained by finger prick. The maximum time and optimum conditions for storage of fresh blood before testing were determined, and the ability of the assay to evaluate cellular immunity to Leishmania was compared to that of the classical Montenegro skin test. A positive correlation between the diameter of the skin induration and the stimulation index was demonstrated. Defining a positive skin test by induration greater than or equal to 5 mm, and a positive proliferation assay by a stimulation index greater than 2.6 and a response greater than or equal to 3000 ct/min, we found a significant correlation between the 2 tests. The proliferation assay was less sensitive than the skin test, but somewhat more specific. Diagnostic specificities and sensitivities did not differ for the 2 tests.