Serum levels of p53 and antipeptide antibody levels to adenovirus type 12 (Ad12) E1b protein were measured in a case-control study of 62 newly diagnosed patients with malignant lymphoma. While patients with gastrointestinal lymphoma did not differ from their matched controls, p53 positive lymphoma patients had significantly (P < 0.04) increased antipeptide IgG antibody levels to the Ad12 E1b. Concomitant detection of serum p53 and antipeptide antibodies to Ad12 E1b was associated with an increased risk (OR = 17.0, 95% confidence limits 1.5, 58.5) of malignant lymphoma suggesting synergism between expression of Ad12 E1b and accumulation of p53 in patients with malignant lymphoma.