A major problem encountered for quantification of IL2 production by stimulated T cells is its simultaneous consumption by these activated cells. In the present study, 40 T-cell clones (TCC) derived from normal peripheral blood, hyperplastic lymph nodes (LN) or lymph nodes involved by malignant lymphomas, were studied for their ability to produce IL2. When supernatants were generated in the presence of 20% fetal calf serum (FCS), no IL2 could be detected for 22 of the 40 TCC, whereas very low levels were found for the 18 other TCC (mean value 31 pg/ml; range from 10 pg/ml to 114 pg/ml); in contrast, when conditioned media were produced with reduced amounts of FCS (final concentration, 1%) as well as in the presence of an anti-CD25 monoclonal antibody (final concentration, 50 micrograms/ml), all TCC were found to release IL2, and very high quantities of this lymphokine were measured (mean value: 11,387 pg/ml; range, from 250 pg/ml to 37,000 pg/ml). Consequently, inhibition of IL2 consumption by PHA-stimulated TCC seems to be an absolute requirement for estimating the true capacity of T cells to produce this lymphokine.