Methods for treating neoplasia, by administering reovirus to a Ras-mediated neoplasm, and use of reovirus for manufacture of a medicament for the treatment of neoplasia, are disclosed. The reovirus is administered so that it ultimately directly contacts cells of the neoplasm. Human reovirus, non-human mammalian reovirus, and/or avian reovirus can be used. If the reovirus is human reovirus, type 1 (e.g., strain Lang), type 2 (e.g., strain Jones), type 3 (e.g., strain Dearing or strain Abney), as well as other sterotypes or strains of reovirus can be used. Combinations of more than one type and/or strain or reovirus can be used, as can reovirus from different species of animal. Either solid neoplasms or hematopoietic neoplasms can be treated.