Cells of Nocardia corallina ATCC 4273 form multiply branched coenocytic mycelia and subsequent fragment to spherical cells when grown on solidified complex media. In liquid shake cultures using complex media the organisms grow into pleomorphic but seldomly branched rods, divide as rods and then the rods fragment to spheres as the stationary phase is reached. In a defined liquid medium with glucose as carbon source, the organisms divide entively as spheres at a doubling time of 44 hrs. The addition of L-tyrosine, some fatty acids and tricarboxylic acid cycle intermediates or fructose to the glucose medium caused the cells to grow at considerably faster growth rates (2.8-8.5 hrs doubling times) and to undergo the shphre-rod-shpere growth cycle. Other amino acids, fatty acids or surgars added singly to the glucose medium did not produce the sphere to rod morphology change. Some amino acids when added to the medium in pairs effected sphere to rod morphopoiesis. None of these amino acids alone were effectors. Some of the culture grew as rods and the remainder as spheres when isoleucine and valine were added to the glucose medium. No other amino acid combination tested gave this result. The reason for the mixed growth response was traced to inhomogeneity of the parent culture. The life cycle of N. corallina is illustrated in a series of photomicrographs of two slide cultures.