The alpha-1-antitrypsin (alpha 1 AT) Pi phenotypes have been determined by isoelectric focusing in a series of 228 patients having a histologically diagnosed malignant lymphoma and in 250 healthy controls. The Pi MZ phenotype occurred in 13 patients with lymphoma (5 . 8%) and in five of 250 healthy individuals (2%). Furthermore, one patient with a Pi SS and three patients with an abnormal unknown phenotype, migrating slower than Z, were found in the lymphoma group. No prevalence for a special lymphoma type was observed among the abnormal Pi phenotype patients. The increased incidence of abnormal Pi phenotypes in malignant lymphoma's support the hypothesis of the possible role of alpha 1 AT in development of immunopathological disorders.