The 24-h culture of bone marrow from patients with acute myeloblastic leukemia (AML) and acute promyelocytic leukemia (APL) gave more analyzable metaphase cells and improved chromosome morphology compared with direct preparations. Culture increased the proportion of cytogenetically abnormal cells, and in six bone marrows where the direct preparation failed, a result was obtained from the cultured preparation. The culture of bone marrow from patients with APL led to the detection of clones carrying the t(15;17) that were not found in direct preparations. Such sequestered clones were not found in AML and acute myelomonocytic leukemia (AMMoL). Cultured preparations were no better than direct preparations from AMMoL.