Zoospores of A. euteiches were attracted to the site immediately behind the root caps of pea roots. The isolation and structural determination of attractant in pea root and its exudates were performed. Isolated attractant was 5, 4'-dihydroxy-7-methoxy-isoflavone, prunetin. This compound was detected both root and its exudates, and strongly attracted A. euteiches zoospore at the concentration 5×10^-7 mol. Prunetin had no attractive effect on A. cochlioides zoospore at the concentrations 10^-5-10^-9 mol.