Cholesterol assimilated by Lactobacillus acidophilus ATCC 43121 was not metabolically degraded in that most of it was recovered with the cells. Cells grown in the presence of cholesterol micelles and bile salts were more resistant to Iysis by sonication than those grown in their absence, suggesting a possible alteration of cellular membranes. Cholesterol assimilation occurred during growth at pH 6.0, the amount of which was more than that by cells grown without pH control. Cholesterol assimilated by cells was recovered in the membrane fractions of cells both grown at pH 6.0 and without pH control. The effect of unsaturated fatty acids on cholesterol assimilation was not clear, since there was no significant (P> 0.05) difference in the amount taken up from micelles prepared using L-${alpha}$-phosphatidylcholine, dioleoyl or L-${alpha}$-phosphatidylcholine, distearoyl. Without Tween 80, little, if any, cell growth or cholesterol uptake was observed. In the presence of 0.05% Tween 80, cholesterol uptake increased dramatically as did growth. However, as the amount of Tween 80 increased beyond 0.05%, cholesterol uptake decreased while the amount of growth remained the same.