Aqueous extracts of asparagus (Asparagus officinalis L.) roots inhibited seed germination in tomato and lettuce, but not in cucumber. The extracts reduced hypocotyl growth in lettuce, shoot growth in asparagus, and inhibited radicle elongation in barley, lettuce, and asparagus. Seedling growth in tomato and two cultivars of wheat were not affected. Inhibition was concentration-dependent. Radicle growth in ‘Grand Rapids’ lettuce was sensitive to an extract concentration as low as 0.05 g dry root tissue/100 ml H2O. Asparagus radicles were more sensitive than asparagus shoots. In one experiment, phytotoxicity of crude extract was not altered by autoclaving. Aqueous root extracts of A. racemosis Willd. also inhibited germination and radicle growth in ‘Grand Rapids’ lettuce. A crude extract was purified by solvent partitioning, and charcoal adsorption, cation exchange, and thin-layer chromatography (TLC). A band from the TLC was found to fluoresce under ultraviolet light, react with phenolic-sensitive localization reagents, and inhibit the growth of lettuce and asparagus radicles.