Preoperative serum immunoglobulins were measured in 102 patients with colorectal carcinoma. There were no differences in the mean values of IgA, IgM or IgG between stages. There was an association, however, between advanced stage of disease and a combination of low levels of IgA (≤200 mg/dl) or high levels of IgM (≥125 mg/dl). The ratio of IgA/IgM was also found to be lower in advanced disease. It was felt that low levels of IgA and high IgM may represent an altered immune response and thus be a prognostic indicator.