The minimal requirements for vegetative growth of Myxococcus xanthus have been sought. Isoleucine, leucine, and valine were required, and vitamin B12 was needed for the synthesis of methionine. Pyruvate was an excellent energy source and an efficient source of cellular carbon. Acetate, aspartate, glutamate, and most tricarboxylic acid cycle intermediates could also be utilized, but were less efficient sources of carbon and energy than was pyruvate. Many mono- and disaccharides were tested, but, in agreement with earlier results, none served as carbon-energy sources. A minimal medium (A1) has been devised that includes the essential amino acids and vitamin B12, with pyruvate and aspartate as carbon-energy sources. In this medium, M. xanthus could propagate indefinitely, and on it vegetative cells formed colonies with greater than 75% efficiency; hence, it is likely that no organic cofactors other than those present in A1 are required in more than trace amounts.