Most (about 81%) of the clinical isolates of shigellae that were tested failed to grow in a minimal medium. Of the auxotrophic isolates belonging to the four Shigella species, 98% grew in a minimal medium containing methionine, nicotinic acid, and tryptophan. The combination of methionine and tryptophan appears to be an obligatory requirement for Shigella dysenteriae serotype 1 strains, while the combination of nicotinic acid and tryptophan appears to be obligatory for serotype 2. Requirements which varied in other isolates were, however, genetically stable, indicating that the auxotypes may be useful as epidemiological markers. Cultures of shigellae in liquid minimal medium containing the above three supplements showed rapid growth and gave reasonably high cell yields.