A 69-year-old man was admitted for the evaluation of leukocytosis with atypical cells. Physical examination revealed marked hepatosplenomegaly. The peripheral blood demonstrated Hb 10.1 g/dl, platelet 13.6 x 10(4)/microliters, and WBC 14200/microliters with 76% lymphoid cells. Bone marrow showed 52.4% lymphoid cells. These cells had a nucleus which was relatively large with a coarse chromatin structure and one prominent nucleolus. Under electron microscopy, these cells had a narrow cytoplasm containing a few mitochondria with some microvilli. The surface of these cells was positive for Ia, B1, B2, C3R, and had markedly elevated IgM-K and IgD-K surface immunoglobulins. Levels of IgG, IgA and IgM were 1140 mg/dl, 53 mg/dl, and 198 mg/dl respectively. He was diagnosed as having B-PLL, and was treated with vincristine, cytarabine and prednisolone. Since B-CLL frequently in accompanied by reduced levels of one or several immunoglobulins, and the most significant is the decrease of IgA, it is speculated from our case that B-PLL is very similar to B-CLL in the abnormalities of B cell function.