beta-Glucosidase (beta-D-glucoside glucohydrolase, E.C. 3.2.1.21, beta-Glu) isozyme variants were studied in a large number of inbred lines, crosses, and races of maize (Zea mays L.). The pattern of Mendelian inheritance demonstrated for beta-GLU variants indicated that they are under nuclear gene control. Twenty-two allelic forms at a single locus were identified in the materials studied by starch gel electrophoresis. Genetic data indicate that beta-GLU in maize is functionally a dimer. Variation of beta-GLU isozymes in 51 racial collections of maize from Mexico showed little correlation with morphological or geographical data. In 39 collections from Central America, variation patterns appeared to have some association with altitude.