Approximately 27 000 maize x tripsacum pollinations were made and 19 hybrids were identified. Fourteen of these hybrids were of the classical type, which possesses the full gametic complement of chromosomes from each parent. These hybrids are more like tripsacum than maize. They are perennial, tiller profusely, and begin to flower in approximately two years from germination. So far, none of these hybrids has produced pollen and all backcrosses have been unsuccessful. Five of the 19 hybrids were not of the classical type, and possessed a variable number of chromosomes in cells of the same root tip. Most cells examined contained 20 maize and no tripsacum chromosomes. Other cells contained 20 maize chromosomes and up to eight of tripsacum. However, in at least three hybrids some cells contained a total of 20 chromosomes, of which up to four were tripsacum substitution chromosomes. These five non-classical hybrids are more maize-like, and are annual. Most have flowered within three months of germination. Although they have produced no viable pollen, four plants have set seed after backcrossing to maize. The production of F1 hybrids is discussed with view to their subsequent assessment and utilization for maize improvement.