In 1993, a serious epidemic of a tomato root disease resembling corky root rot occurred in commercial greenhouses throughout Canada. Pyrenochaeta lycopersici could not be isolated from diseased roots, but Humicola fuscoatra was commonly isolated. The objectives of our work were to determine if H. fuscoatra is able to infect roots of tomato and cause corky root rot symptoms. Humicola fuscoatra was found to infect the roots of tomato seedlings and older plants. We concluded that H. fuscoatra is not a pathogen of tomato, however, because infection of tomato roots with the fungus did not necessarily lead to development of corky root rot or any other disease symptoms. Populations of H. fuscoatra increased greatly in sterile water or sterile nutrient solution, which would help to explain why commercial greenhouse growers can find this fungus in recirculating nutrient solutions.