Lysophospholipid acyltransferases (LPATs) catalyze the addition of an acyl chain to a lysophospholipid to form a phospholipid, dramatically altering lipid structure and behavior. These changes influence membrane curvature, the processes of vesicle and membrane tubule biogenesis, and the structure and trafficking dynamics of secretory organelles. At the beginning of my studies, I investigated the synergistic and antagonistic relationships between the activities of LPATs and phospholipases in regulating membrane trafficking. I went on to identify, by performing an overexpression screen, the human LPAT isoforms that are most important for regulating secretory membrane trafficking. I chose one of these enzymes for further characterization, the human membrane bound O-acyltransferase (MBOAT) gene family member lysophosphatidylcholine acyltransferase 3 (LPCAT3). Using selective membrane permeabilization immunostaining, I determined the topological orientation of LPCAT3's 11 transmembrane domains and luminal active site. I also found that a C-terminal K(x)KXX motif was necessary for LPCAT3 localization to the endoplasmic reticulum (ER). I observed the influence of LPCAT3 activity on the structure and dynamics of the early secretory system, through overexpression which reduced soluble protein secretion to 22% of control and caused relocalization of COPI and COPII vesicle markers. Additionally, LPCAT3 knockdown had profound effects on retrograde trafficking from the Golgi and ER-Golgi intermediate complex (ERGIC) to the ER. Knockdown slowed trafficking of the p58 receptor (ERGIC-53) and Brefeldin A induced recycling of Golgi phosphoprotein of 130 kDa to the ER. Slowed retrograde transport was accompanied by increased membrane tubulation. These effects of knockdown were reflected in the localization of ERGIC-53 and markers of COPII and COPI vesicles, which were mislocalized in knockdown cells. However, the alteration of LPCAT3 expression levels, through knockdown or overexpression, did not disrupt the morphology of the Golgi complex, trans-Golgi network (TGN), adaptor protein 1 (AP-1)/clathrin-coated vesicles, or endosomes. These results suggest that LPCAT3 activity is important for efficient COPI vesiculation, the production of retrograde membrane tubules, and the fusion of retrograde membrane tubules with the ER. These findings support a novel role for LPAT activity in the regulation of COPI function, membrane tubulation, and retrograde trafficking to the ER.