Long-term cultures (LTC) were established from chronic myeloid leukemic bone marrow or blood. As detected by immunocytochemistry using 25 different monoclonal antibodies, the in vitro cultured cells express a variety of adhesion molecules and differentiation antigens. beta 1 and beta 2 integrins are constantly present on long-term cultured cells. CD4, CD54, CD58, and CD71 markers become highly expressed on the cells after about 10 days in vitro while CD56 is permanently lacking. Only 5 of the 17 patients studied had between 25 and 85 per cent CD33 and CD34 differentiation antigen-positive cells initially in the bone marrow or blood. There was a decrease to less than 10 per cent after six to eight weeks in culture. In later stages of long-term culture, monocytes/macrophages become the dominating cell types. Blast cells are admixed to these cells in varying numbers. In 4 of the 17 cases studied long-term cultures converted to cell lines showing indefinite cell growth. The cells were identified as B cell blasts spontaneously transformed by Epstein Barr virus (EBV). The permanent myeloid and monocytic leukemia cell lines K-562, HL-60, KG-1, RC-2a, CTV-1, THP-1, and U-937 were likewise tested for adhesion molecules and differentiation antigens. A stable marker expression was found, the pattern of which is characteristic of each cell line. CD4 is frequently present on myeloid and monocytic leukemia cell lines (HL-60, RC-2a, THP-1, and U-937). Exceptionally, CD2 and CD34 were shown on KG-1. CD49e, CD49f, CD44, and CD71 are expressed on all cell lines tested.