some factors affecting the expression of epsteinbarr virusassociated membrane antigens the effect of two factors larginine concentration and phytohemagglutinin pha stimulation on the expression of epsteinbarr virus ebvassociated membrane antigens ma was evaluated an ebvproducer cell line av1 was cultivated in eagles basal medium with earles salts supplemented with various larginine concentrations ranging from 00 to 200 mm in most of the larginine concentrations the number of cells expressing ma decreased within the first 24 hours this decrease was followed by a marked increase in mapositive cells at 48 hours and a slight decrease between 48 and 72 hours statistical evaluation however revealed no significant differences in the level of ma expression among cells exposed to the various larginine concentrations these findings were discussed in relation to the cell cycle dependence of largininedeficient media as a virusactivating agent av1 cell cultures were treated with pha and observed at 24hour intervals for 72 hours within the first 24 hours the percentage of cells showing ma was markedly increased this was followed by a rapid decline in percentage of mapositive cells within the next 24 hours treatment of an ebvnonproducer cell line nc37 with pha resulted in the production of ma in approximately 11 of the cells within the first 24 hours the number of mapositive cells gradually declined over the next 48 hours no viral capsid antigens were detected in these cells the data suggested either complete or partial activation of the latent ebv genome by pha