Collection and description of the maize (Zea mays L.) germplasm complexes of Mexico began in 1943, and efforts toward the potential utilization of the 25 recognized Mexican races were initiated in 1961. This study was conducted to determine the performance of the 25 Mexican races and 300 interracial crosses evaluated in three environments identified as high (2249 m), intermediate (1800 m), and low (1300 m) elevations. Data were analyzed with the Gardner‐Eberhart model, Analysis II. At the high elevation the races Cónico, Cónico Norteño, and Chalqueño had high mean yields per se and in crosses. Cacahuacintle and Maiz Dulce had equally high yield in crosses but had lower per se yield. At the intermediate elevation, the best yielding races in crosses and per se were Comiteco, Harinoso de Ocho, Celaya, Maiz Dulce, Tabloncillo, and Tuxpeno. At the low elevation, the highest per se yields were exhibited by Harinoso de Ocho, Celaya, Pepitilla, and Tabloncillo. Across all elevations, the best general combiners were Cacahuacintle, Harinoso de Ocho, and Maiz Dulce. Results of this study could be used to (i) introgress the heterotic patterns found among races into new commercial varieties or populations, (ii) search for race collections with better agronomic type that belong to the racial heterotic pattern, (iii) improve gene pools based on racial heterotic patterns and geographical origins, (iv) establish reciprocal recurrent selection between two races that exhibited heterosis when crossed, or (v) develop hybrids based on lines derived from the collections studied in each environment.

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Synopsis Visual selection during successive generations of inbreeding in corn resulted in significant improvement in yield, ear appearance and plant appearance by 57%, 60% and 41%, respectively, of the 134 specific hybrid combinations. The visual selection for yield and ear appearance was more effective in introduced than in local, well‐adapted lines. For plant appaarance the visual selection was more eftective in local, well‐adapted lines.