Antibody systems were produced in rabbits by immunization with antigen systems from seed ofZea mays, Z. mexicana andTripsacum dactyloides. Antigen systems were generally ranked in the following order using Zeaantibody systems: Zea > Tripsacum > Elyonurus ≈ Bothriochloa > Coix ≈ Manisuris > Andro-pogon ≫ Triticum. Tripsacum antibody systems also ranked these antigen systems in a similar order except that Tripsacum > Zea, and Manisuris ≈ Bothriochloa ≈ Elyonurus. Some Tripsacum species produced anomalous results. Serology suggests that Zea and Tripsacum should be placed together in the subtribe Tripsacinae of the tribe Andropogoneae: the tribe Maydeae is probably an unnatural assemblage. Tripsacum and Zea have probably evolved from ancestors with affinities to the subtribes Rottboellinae and Bothriochloeae of the tribe Andropogoneae. The high degree of serological correspondence shown by Elyonurus to Zea suggests a close common ancestry, but Manisuris appears no more similar to Tripsacum than do other genera of the Rottboellinae and Bothriochloeae. By polyacrylamide gel electrophoresis, no differences were found between maize and teosinte from Mexico and north Guatemala. Teosinte from south Guatemala consistently lacked bands present in both maize and Mexican teosinte but shared no greater similarity to Tripsacum and cannot therefore be considered as tripsacoid. The high degree of band homology between maize and Mexican teosinte supports a parental relationship and it is suggested that Mexican teosinte represents the germ plasm from which maize was domesticated. Neither electro-phoretic nor serological results supported the hypothesized hybrid (viz. Zea x Manisuris) origin of Tripsacum.