Suspension cultures of finely divided soybean cells established from callus were incubated with sodium [1(14)C] acetate for periods up to 86 hr. Lipids and fatty acids were analyzed for radioactivity in samples harvested at logarithmic time periods. Incorporation of acetate into cell lipid was directly proportional to the logarithm of time up to 32 hr, after an initial lag of 4-6 hr. Most of the lipid radioactivity was found in the phospholipid fraction, and all common soybean fatty acids became labeled within 6 hr. The order of labeling and distribution of radioactivity with time were essentially the same as in tissues from intact growing plants. These results support the concept of sequential desaturation of oleic acid in the cells. It was concluded that valid studies of the biosynthesis of common lipids in the soybean can be carried out for extended periods of time by use of undifferentiated cells in suspension cultures.