This proposal is for a case-control study of multiple myeloma in Los Angeles County. The case-group will include 440 cases, 340 whites and 100 blacks, of multiple myeloma identified by the Los Angeles County/USC Cancer Surveillance Program and interviewed by telephone over a five-year period. Controls will be neighborhood controls from the residence of the case at diagnosis who are matched to the case on date of birth (+5 years), sex, and race. The major hypothesis to be tested is that the etiology of multiple myeloma is related to chronic antigenic stimulation especially in conjunction with underlying immune abnormality, either genetically or environmentally determined. The following major subject areas are addressed by the questionnaire: occupational exposures, radiation exposure, hormonal status, medical history, family medical history. We plan to compare risk factors in men and women and in blacks and whites and by class of immunoglobulin (IgG or IgA) secreted by the malignant cells.