A 3-year field experiment (1976 through 1978) was conducted at Yuma, Arizona and Logan, Utah to determine the effects of environment on growth and grain yield of Siete Cerros and Cajeme 71 wheat (Triticum aestivum L.) geotypes grown under irrigation. The growing seasons were December to June in Arizona and April to August in Utah. Siete Cerros produced taller plants and higher straw and grain yields than did Cajeme 71; however, Cajeme 71 required fewer days from planting to flowering and flowering to maturity, at each location each year. Cultivars grown in Arizona produced taller plants, more straw, and more grain than the same cultivars grown in Utah; however, both cultivars required more days from planting to flowering and fewer days from flowering to maturity in Arizona than they did in Utah. Some plant growth characteristics of both cultivars varied from year to year but the variations were not consistent enough to suggest genetic differences between cultivars, except for plant height. This foregoing research suggested that a 3-year period was not long enough to indicate genotype-environment interactions; however, it may be safe to conclude that spring wheat cultivars may quickly adapt into high yielding winter annuals in irrigated, semiarid regions like Arizona. Additional Index Words. Genotypes, Varieties, Plant Adaptation, Plant Culture.