We recently demonstrated that expression of BHMT in McArdle RH-7777 (McA-BHMT) cells increases apo B mRNA abundance, leading to parallel increases in apo B secretion, The ratio of unedited to edited apo B mRNA was unchanged by BHMT expression, Based on the observation that secretion of B48 is increased relative to B100 in McA-BHMT cells, current studies now include comparison of B48 and B100 synthesis and intracellular degradation. Minor differences in co- and posttranslational degradation were unable to account for relative increase in B48 secretion, and the disappearance kinetics of B48 were similar in McA-BHMT and control cells. Consistent with the increase in endogenous apo B mRNA in McA-BHMT cells, B48 synthesis is increased significantly. in contrast, synthesis of B100 was not significantly increased. We conclude that B48 is preferentially translated compared to B100 when endogenous apo B mRNA is increased.