Exposure to the plant Euphorbia tirucalli has been proposed to be a cofactor in the genesis of endemic Burkitt's lymphoma (eBL). The purpose of this study was to examine the effects of unpurified E. tirucalli latex on Epstein-Barr virus (EBV) gene expression. A Burkitt lymphoma cell line was treated with varying dilutions of the latex and the effects on EBV gene expression were measured. We observed that the latex was capable of reactivating the EBV lytic cycle in a dose-dependent manner and at dilutions as low as 10(-6). Simultaneous treatment of cells with E. tirucalli latex and the protein kinase C inhibitor 1-(5-isoquinolinesulphonyl)-2-methylpiperazine dihydrochloride blocked lytic cycle activation. These data suggest that environmental exposure to the latex of E. tirucalli could directly activate the EBV lytic cycle and provide further evidence of a role for E. tirucalli in the aetiology of eBL.