Parthenium hysterophorusL. (parthenium), an obnoxious Asteraceous weed, has spread over millions of hectares of land in India after its inadvertent introduction in the 1950s. This weed has reduced the yield of grasses and crops. It is a health hazard to sensitized humans and cattle and the routine weed control methods have failed to check its spread.Cassia unifloraa leguminous undershrub of some economic value, is found to suppress the growth of parthenium. It has successfully replaced parthenium by over 90% in an area of 4800 m2over a period of 5 years. While the leachates from the germinating seeds ofC. uniflorainhibited the germination of parthenium seeds and hampered the establishment of summer generation of parthenium due to allelopathy, the robust colonies ofC. unifloraprevented the establishment of winter generation of parthenium below them.Cassia uniflorais dispersed slowly to neighbouring places through rainwater. Sustained efforts to introduceC. uniflorahold out great promise of parthenium control, and by adapting this method financial benefits are also expected to accrue in the course of time.