Since 1951 when our taxonomic study of the genus Nocardia began, only eight strains of N. carnea (Rossi-Doria) Castellani & Chalmers, four strains of N. vaccinii Demaree & Smith, five of N. transvalensis Pijper & Pullinger, 21 or N. orientalis (Pittenger & Brigham) Pridham and 14 of N. aerocolonigenes (Shinobu & Kawato) Pridham have been found. These five groups of strains are described and are compared with strains of nine accepted species of Nocardia. With the possible exception of N. orientalis, more strains of these five taxa must be assembled and examined to establish the reliability of our descriptions and identifications.