Fusarium oxysporum is the causal agent of vascular wilts in many different plant species. The components of the interaction between pathogen and plant that lead to susceptibility or resistance to disease are receiving intensive study. It is evident that F. oxysporum produces proteins which can kill plant cells and may function in plant/ pathogen interactions. A 24 kDa protein which causes necrosis in leaves of many dicots was purified from F. oxysporum culture fitrates. Related 24 kDa proteins are produced in the culture filtrates of many F. oxysporum isolates including several formae specialis. A 22 kDa xylanase originally isolated from Trichoderma viride was identified in culture filtrates of F. oxysporum. The xylanse induces many different defense responses in tomato and tobacco with an activity that is independent of the xylanase enzyme activity and apparently dependent upon a protein/protein interaction with a plant membrane protein. A pair of proteins, 56 and 61 kDa in size, were purified from culture filtrates of F. oxysporum f. sp. lycopersici race 1 which cause death of tomato cells lacking the I1 gene which gives resistance to race 1 of the pathogen. In this case the proteins are thought to function as toxins. A 59 kDa glycoprotein has been isolated from spores of a F. oxysporum f. sp. vasinfectum race 1 isolate which has biological activity in a cotton variety resistant to race 1. This interaction closely resembles an elicitor/receptor model where the fungal protein acts as an avirulence factor which is recognized by a receptor in an incompatible interaction. The proteins discussed here demonstrate the wide range of activities and specificities proteins produced by F. oxysporum can have in plants and plant/pathogen interactions.