The objective of this study was to estimate a novel apoptosis-promoting molecule PDCD5 expression in the bone marrow cells from adult acute myeloid leukemia (AML) for investigation of its significance in the pathogenesis of AML. Flow cytometry assay was used for detection of PDCD5 expression in the different groups of cells from bone marrow of AML patients and normal controls by using 21 monoclonal antibodies with different fluorescent markers. The PDCD5 expressions in bone marrow cells from some AML patients and normal controls were also detected by Western blot. The results showed that the mean PDCD5 fluorescence intensity in bone marrow nucleated cells (MNC) from the bone marrow of 36 untreated AML patients was significantly lower than that from the bone marrow of 30 normal controls (3059 +/- 1392) vs (7432 +/- 1261) (P < 0.01). The mean PDCD5 fluorescence intensity was lower in the marrow granulocytes, monocytes, blast cells, and lymphocytes from untreated AML patients than that from normal (3939 +/- 2121) vs (8367 +/- 1045); (3156 +/- 1635) vs (5917 +/- 2329); (2824 +/- 1592) vs (3998 +/- 2106); (1474 +/- 816) vs (3355 +/- 2042) respectively, (all P < 0.01). Western blot analysis demonstrated that PDCD5 expression was significantly decreased in the AML cells, as compared with normal cells. It is concluded that PDCD5 expression in MNC in untreated AML patients is lower than that in the normal. PDCD5 expression in the marrow granulocytes, monocytes, blast cells, and lymphocytes of untreated AML patients is significantly lower than that in the normal. It suggests that the abnormally low expression of PDCD5 may be involved in the pathogenesis of AML.