Antigen- and Concanavalin A-induced culture supernatant have been reported to contain inhibitors of interleukin 2 (IL2) activity which necessitate concentration of samples over Amicon membranes prior to lymphokine assay. However, since we found this to be unnecessary, we have re-evaluated the effects of Amicon and millipore membranes upon the lymphokine litres of such supernatants. Our findings do not support the notion of an IL2 inhibitor, but indicate that lymphokine levels can be dramatically reduced as a consequence of millipore filtration.