Reproducible Chinese-hamster bone marrow and spleen cell culture preparation systems for sister chromatid exchange and chromosomal aberration analyses were described. These systems can be used for in-vivo and partial in-vivo comparison studies and can also be used for in-vitro genotoxicity assays. Either the animals or cells can be exposed to compounds being tested. After treatment, cells can be cultured for cytogenetic analysis. For this method, Chinese- hamsters were killed by cervical dislocation. Bone marrow was flushed from femora and tibia and centrifuged to collect the bone marrow cells. About 1,000,000 cells were cultured with a complete medium. Spleens were obtained aseptically, transferred to centrifuge tubes, and mashed with a sterile spatula. Cells were collected by low speed centrifugation. About 1,000,000 cells were suspended with complete medium. Cultures for sister chromatid exchange analysis had 5-bromo-2'-deoxyuridine added for 24 to 48 hours for bone marrow cells and 36 to 40 hours for spleen cells. The method was validated with different genotoxic agents for partial in-vivo studies.