Liposomes containing phosphatidic acid (PA) and inclusion complexes of PA with methyl-P-cyclodextrin (CD) were compared with PA dispersion prepared with a nonionic surfactant, Tween 80, for their effect on the growth of Chinese hamster ovary (CHO) cells in serum-free culture. All of the types of PA preparation were capable of promoting cell growth to almost the same high extent, indicating that the efficacy of PA in stimulating cellular growth may not depend on the preparation method.