||Conserving traditional maize (Zea mays L.) landraces grown by farmers in Latin America can con- tribute to food security. Core subsets of such landraces that represents that diversity can be used for their en- hancement. One such enhancement effort was conducted on a total of 81 accessions drawn from the CIMMYT maize collection of the race Zapalote Chico and newer accessions collected in 1999 from Istmo de Tehuantepec, Oaxaca, Mexico, where the race Zapalote Chico is pre- dominantly grown. These accessions were evaluated at four locations in the Mexican states of Morelos, Guerrero, and Oaxaca for agronomic and morphological traits to as- sess the intraracial diversity for conservation and en- hancement. Eleven agronomic and morphological traits were measured and used for a multivariate cluster analy- sis. The cluster analysis produced four non-overlapping clusters with 63 accessions, indicating the intraracial di- versity of the Zapalote Chico. The analysis also formed two other clusters with four races, including Tepecintle and Olotillo, which have been introduced to the region of Istmo de Tehuantepec. Using a selection index that ac- counts for grain yield, grain quality, and standability, and an agronomic performance rating, a breeder core subset (the best 20%) was chosen to represent phenotypic diver- sity among the clusters. In the core subset, fifteen acces- sions comprise the core subset of the race Zapalote Chico and three accessions comprise the core subset for the other races. These core subset accessions, which repre- sent the diversity of the regional landraces of maize, can be enhanced through introgression of improved lines or populations for yield potential, drought resistance, and ear rot resistance, while maintaining the desirable grain quality traits of the original races.