In PBM obtained from 24 immunodeficient patients (two severe combined immunodeficiencies, three cases of Wiskott-Aldrich syndrome, two immunodeficiencies with hyper IgM, three cases of X-linked agammaglobulinemia, and 14 common variable immunodeficiencies) and from 19 age-matched controls, we have studied 1) the proliferative response to optimal and suboptimal doses of PHA after “in vitro” supplementation of the cultures with mitogen-free supernatants containing II 2 (IL 2 Sup), and 2) the production of IL 2 in response to an optimal dose of PHA.

Addition of IL 2 Sup to cultures of normal PBM stimulated with 1% or 0.05% PHA did not cause significant augmentation of proliferative response, and only at a very low PHA dose (0.02%) did the addition of IL 2 Sup induce an increment of the DNA synthesis. On the other hand, addition of IL 2 Sup to lymphocytes from immunodeficient patients stimulated with the suboptimal dose of PHA (0.05%) caused an enhancement of the DNA synthesis, which in most cases never reached the levels ob-served in normal individuals, and was more manifest in those patients who showed a PHA response below the normal level.