Rat hepatocyte monolayer triglyceride content was increased modestly by incubations with apolipoprotein E-containing triglyceride emulsions or chylomicrons (exogenous) and was increased substantially by increasing media free fatty acid concentrations (endogenous). The secretion of both endogenous and exogenous triglyceride into media was enhanced by additions of serum and serum components. These additions not only enhanced hepatocyte triglyceride secretion but also, because of the absence of media lipolysis, more triglyceride was recovered in the system. Lipoprotein-free serum replicated the effect of whole serum. Lipoprotein produced a more modest secretory response. The apolipoprotein C components were the only ones that enhanced hepatic triglyceride secretion. Both lipoprotein-free plasma and lipoprotein enhanced the in vitro transfer of hepatocyte exogenous triglyceride to fibroblast.