['Reduced expression of HLA class I molecules has been demonstrated for many human neoplasias and is correlated with increased malignancy.', 'We investigated the correlation between HLA expression on blasts and the number of peripheral blood leukocytes (WBC) at onset in 34 patients with acute non lymphoblastic (ANLL) leukemia. Leukemic blasts at onset were serologically typed for HLA-A,B specificities, and the patients were classified in three groups according to the number of detectable surface HLA antigens.', 'The amount of WBC at onset in patients lacking HLA antigens was significantly higher than in patients with no antigenic loss.'] Is loss of surface HLA class I molecules in leukemic myeloblasts correlated with an increased leukocyte concentration at onset?