Investigation for possible chemical interactions among some ofrnthe common grass species that grow in and around Addis Ababa was undertaken.rnThe species used were the grasses Alldropogon abyssinicus R. Br. ex Fl:Â·esen,rnHyparrhenia arrhenobasis (Hochst. ex. Steud.) Stapf, Pennisetum glabrumrnSteud., SnOl"ldenia polystachya (Fre san) Pi Ige1', E leusine jaegeri Pi Iger,rn&ragrosti8 tenuifolia (A. Rich) Steud. and a legume, ~!edicago polymorpha L.rnThe effects of the extracts of the seven species on the seedrngermination and plumule and radicle growt'h of the same seven species shoW}drnthat ~. abyssinicus and ~. polystaohya were the most inhibitory followed byrnH. arrhenobasis and .!!!... jaegeri in that order. Extracts from!!!... tenuifolia,rnH. polymorpha and P. glabrum showed less inhibitory effects than the abovernspecies.rnSee.d germination inhibition effect Was greatest on ~. polystachyarnand P. glabrum and that on E. jaegeri and H. arrhenobaaia '"aa the least.rnAuto-inhibition ,"as found to be as high as allo-inhibition. Extractsrnfrom all the species except!!!... tenuifolia ShOfed auto-inhibitory effecta onrngermination and plumule growth and/or radicle grovlth.rnDifferent experiments Vlere carried out to detect the fay of releasernof the inhibitory chemical(s) in ~. abyssinious. The results obtained fromrnthese experiments indicate that !. abyssinicus inhibits other speoies whenrndecomposition of its dead .remains takes place and that the live plant dossrnnot re lease any alle lopathic st'bstance into the soil medium