CD2 expression in murine B cell lineage was examined by flow cytometric and immunoprecipitation studies with anti-murine CD2 mAb and by Northern blot analysis. Cell surface expression of CD2 was demonstrated on all peripheral B cells and cell lines of B lineage. The murine CD2 transcript of 1.3 kb was detected in these B cells. An identical glycoprotein of 55-67 KD was precipitated from the lysates of surface radioiodinated thymocytes, splenic T and B cells, T and B lymphomas, RL male 1 and BCL-1, with anti-murine CD2 mAb. The majority of bone marrow B cells and a half of pre-B cells were found to be positive for CD2 expression. These results indicate that murine CD2 is expressed on B cell lineage at certain differentiation stages.