Bone marrow samples from patients with various hematologic disorders were stored at 4 degrees C for up to 5 d before the establishment of a 24-h culture. We tested various factors, including storage time, colony stimulating factor, and methotrexate in an effort to improve metaphase and chromosome quality. Cytogenetic findings for various hematologic diseases were compared in a total of 201 cultures. Cold storage for up to 3 d did not seem to adversely affect the number of mitoses or the quality of chromosome banding when cells were cultured in a system that used both colony stimulating factor and methotrexate. In samples studied in parallel, clonal abnormalities were noted as frequently in cells stored in the cold as in those processed directly.