A state of immunosuppression or immunodeficiency has been described after surgical trauma. Cellular immune functions are more heavily affected. At present the relationship between these abnormalities and the increased incidence of infections in surgical patients has not been clarified. The activation of the humoral compartment and the appearance of lymphoblastoid B cells spontaneously secreting IgG and IgA have been observed in surgical patients. These cells are a marker of a recent antigenic exposure. In this study the kinetics of appearance of this B cell subset and the relationship between spontaneous Ig secretion and DNA synthesis have been analysed in six cholecystectomized patients. A peak of spontaneous IgG and IgA secretion is evident 5 and 7 days after the intervention. In some patients (two out of six) the appearance of lymphoblastoid B cells is cyclical. A second wave of spontaneous Ig secretion becomes evident 14 days after surgery. Double immunofluorescent staining of peripheral blood lymphocytes for BrdU and cytoplasmic Ig (cIg) was employed to demonstrate that a fraction of lymphoblastoid B cells is actively proliferating and that other cells negative for cIg but active in DNA synthesis appear in the circulation. These data confirm the signs of activation observed after elective surgery in otherwise healthy subjects.