Seed of yellow foxtail(Setaria lutescens(Weigel) Hubb.) biotypes collected in Connecticut, Iowa, Massachusetts, Pennsylvania, and California were grown under field conditions at Davis and Woodland, California. Three biotypes collected in California alfalfa(Medicago sativaL.) fields all exhibited only a prostrate growth habit; the biotypes from the eastern United States all had an upright growth habit. The California biotypes were always glaucous; those collected in the east were not glaucous. Ratio of culm height to culm length were near unity for the eastern biotypes but averaged 1.5 to 1.7 for the California biotypes. Variations existed between biotypes in days from planting to heading, number of nodes per culm, leaf shape and size, and in final dry weight per plant.