This interview study included 136 Los Angeles County residents aged 20-69 with CML diagnosed from 1979 to 1985 (cases) and 136 neighbourhood controls. During the 3-20 years before diagnosis of the case, more cases than controls had radiographic examinations of the back, gastrointestinal (GI) tract and kidneys, and cases more often had GI and back radiography on multiple occasions (odds ratio (OR) for back X-rays on five or more occasions = 12.0; P less than 0.01). Published estimates were used to assign a minimum dose to the active bone marrow for various radiographic procedures. ORs were estimated for cumulative marrow doses for each of four time periods (3-5 years, 6-10 years, 11-20 years and 3-20 years before the diagnosis of the case). The ORs for exposure to 0.99, 100-999, 1000-1999 and greater than or equal to 2000 mrad in the 3-20 years before diagnosis were 1.0, 1.4, 1.6 and 2.4 (P for highest exposure category and P for trend both less than 0.05). The association was strongest for the period 6-10 years before diagnosis, and the effects of radiation exposure during this period remained significant after consideration of other risk factors in a logistic regression analysis.