Development of a short term assay for lymphoblastic transformation in man. Blastic stimulation of lymphocytes by antigens or mitogens is usually measured by 3H-TdR labelling of DNA synthesis in 4 to 7 days. However, it has been recently shown, first in mice and guinea pigs, then in men, that it is possible to detect an earlier event by measurement of protein synthesis with 3H-Leucine in a few hours. The work presented here is devoted to determine the optimal conditions of such a short term assay in man. The technique we propose is described. Preliminary clinical results in lymphomas patients, compared to "in vitro" skin tests, are encouraging.