We have shown previously that cycloheximide (CHX), a potent protein synthesis inhibitor, induces high levels of apoptosis in Epstein-Barr virus free (EBV(-)) Burkitt's lymphoma (BJA-B) cells, with comparably reduced levels of apoptosis in the EBV positive (EBV(+)) cells. Modulation of CHX-induced apoptosis in EBV(-) and (+) B cells is reported here using concurrent treatment with phorbol ester (phorbol 12, 13-dibutyrate, PdBu). Cells were collected at 0, 3, 6, 12, 24 and 48 hours after treatment with (i) 1 microgram/ml CHX, (ii) 0.1 microgram/ml PdBu (1 hour pretreatment before 0 h), or (iii) CHX + PdBu (CHX added at 0 h, 1 hour after PdBu). Control cultures were untreated. Apoptotic, necrotic or viable cells were quantified using histological, ultrastructural and biochemical parameters. Protein synthesis was assessed using 35S-methionine incorporation. Intracellular calcium concentrations were measured using flow cytometry. PdBu alone had little effect on cell death: High levels of CHX-induced apoptosis in EBV(-) cells were significantly reduced by concurrent addition of PdBu (P < 0.005). In contrast, low levels of CHX-induced apoptosis in EBV(+) cells were not significantly altered by PdBu treatment. In EBV(-) cells, a negative relationship was observed between levels of apoptosis and calcium concentrations, whereas in EBV(+) cells, there was negligible correlation between these parameters. Thus high levels of CHX-induced apoptosis in EBV(-) cells occur via a PKC-dependent pathway, whereas CHX treatment of EBV(+) cells induces comparatively low levels of apoptosis that occur via a PKC-independent mechanism. The results application in the therapeutic intervention for cancers developing in association with EBV infection.