INTRODUCTIONThe majority of mouse chromosome preparations for banding are now made by air-drying and, in essence, require the production of a cell suspension as a starting point. Some samples such as blood cultures, ascitic fluids, or cells growing in suspension will already be in suspension; others, such as bone marrow, solid tumors, or cells growing as attached layers in culture must be converted to suspensions. The basic steps in karyotyping and banding embryonal carcinoma cells are outlined below.