We analyzed the expression of the VpreB gene in 5 common variable immunodeficiency (CVI) patients. There was no deletion or large mutation as compared with control DNA by Southern blotting. In the peripheral blood mononuclear cells of CVI patients, expression of the VpreB gene was not detected by polymerase chain reaction. These results suggest that there were no immature B cells such as pro- or pre-B stages in the peripheral blood mononuclear cells of these CVI patients. In B lymphoblastoid cell line (LCL) cells, expression of VpreB gene was observed in patients and Manca cells. The results suggest that the stages of these LCL cells may be a traditional stage between pre-B and mature B cell. As for the Manca cell, our result is in accordance with a recent report that surface immunoglobulin-positive cell lines also express the pre-B-related genes.