The release of platelet-activating factor (PAF)-like material was evaluated from eight B and T human leukemic cell lines and from three lymphoblastoid cell lines obtained after Epstein-Barr virus (EBV) transformation. All cell lines were stimulated with ionophore A23187, phytohemagglutinin (PHA), or both either in the presence of or without acetyl coenzyme A (AcCoA). After appropriate stimuli, all cell lines tested released PAF-like material, irrespective of the surface phenotype and of the level of differentiation. Some cell lines released PAF-like material after stimulation with A23187 (Molt-4, Jurkat, 1301, Raji, FM007), others only if AcCoA was added to A23187 (CCRF/CEM, HUT 78, Daudi, Nalm-1). In some cases, PHA was capable of enhancing the effect of A23187 (Molt-4, HUT 78, Daudi, IBW4) and finally, in a lymphoblastoid cell line (WT20), the release of PAF-like material was achieved only in the presence of both A23187 and PHA. These findings demonstrate for the first time that human lymphoid cells both of B- and of T-cell origin can release a PAF-like material after appropriate stimuli.