Data from two completed case-control studies of agranulocytosis and aplastic anemia, the International Agranulocytosis and Aplastic Anemia Study (IAAAS), conducted in Europe and Israel, and a similar but smaller study conducted in the United States, will be combined and analyzed together. The studies had as a main focus the evaluation of drugs in the etiology of the dyscrasias; data were collected over a 12-year period (1979-1991), using the same methods, including the same interview questionnaire. The combined data would include 31% more cases of agranulocytosis, 77% more cases of aplastic anemia, and 188% more controls than were available when the main results of the IAAAS were published. The increase in numbers will allow the evaluation of drugs for which there were previously insufficient numbers of exposed cases or controls, The quantification of previously reported associations with increased precision, and the documentation of absence of associations. Where feasible, we will examine possible dose-response relations (duration effect) and effect modification by factors such as age and sex. We will also examine associations with nondrug factors including occupational exposures, medical history, and lifestyle factors. These data were collected at great expense; there are no funds available to support the combined analyses, which will considerably enhance the already published results. The logistical and methodological issues have already been resolved through our experience with both studies.