Preoperative serum levels of secretory IgA (SIgA) and secretory IgM (SIgM) were quantified by an enzyme-linked immunosorbent assay in 100 patients with large bowel carcinoma. The values obtained were related to tumor characteristics such as Dukes' stage, differentiation, DNA ploidy pattern, expression of secretory component (SC), volume, and plasma level of carcinoembryonic antigen (CEA). Statistical comparison was made with matched controls. Only patients with Stage D tumors showed significantly increased serum levels of SIgA and SIgM (P less than 0.004). The combined diagnostic sensitivity of SIg and CEA in Stage D was 0.94. In patients with liver involvement, serum SIgA and SIgM were elevated in 67% and 53%, respectively. However, circulating SIg was neither correlated with tumor SC expression nor with any other studied variable. Thus, the raised serum SIg levels were apparently not caused by release of SC from the tumors but, instead, by hampered liver function due to hepatic metastasis.