BACKGROUND In lymphoproliferative diseases the expression of Bcl-2, a mitochondrial oncoprotein capable of blocking apoptosis, is well-documented, while little research has been carried out on its distribution in myeloproliferative conditions. METHODS Using immunocytochemical methods, 63 cases of acute myeloid leukemia (AML) at onset and 10 relapses were studied to investigate Bcl-2 expression and any possible correlations with subtypes of the FAB classification, sex, age or white cell peripheral blood count at onset. RESULTS Bcl-2 is present in 87.3% of AML cases at onset and in 100% of relapses. In 68.3% of cases at onset and in 90% of relapses the protein is present in more than 20% of the blasts. Relapses always show higher percentages of positive expression than those seen at onset. Our results demonstrate no statistical correlations between the expression of the oncoprotein Bcl-2 and FAB subtypes, sex, age, or white cell peripheral blood count. CONCLUSIONS The majority of blasts from AML patients express the oncoprotein Bcl-2, which is able to protect leukemic cells from apoptosis. Since numerous chemotherapies are cytotoxic in that they induce apoptosis, we feel that in vitro studies of cells from AML patients are necessary in order to broaden our knowledge about the effects of the most common therapeutic drugs and of those substances which, alone or in association, can modulate Bcl-2 expression.