Anaplastic large cell lymphoma (ALCL) is usually composed of large pleomorphic cells, which express CD30 antigen and the epithelial membrane antigen (EMA). These tumour cells tend to occur in younger patients and may be associated with cutaneous and extranodal involvement. A proportion of these cases contain a chromosomal translocation t(2;5) (p23; q35). These results in a hybrid gene encoding part of the nucleophosmin (NPM) gene joined to the cytoplasmic domain the anaplastic lymphoma kinase (ALK) gene, giving rise to the protein, p80. Large cell lymphomas account for approximately 25 per cent of all non-Hodgkin’s lym phomas in children and young adults, of which one third carries the NPM-ALK gene translocation. This antibody may be used to detect p80 in these lymphomas. In addition, this antibody may also be used to detect a recently described subtype of large B cell lymphoma, which expresses the full-length ALK protein.