To evaluate chemical safety, many kinds of short-term mutagenicity assays are performed together with long-term assays in animals. Rationales and methodology for these assays have been well discussed and documented. No statistical method, however, has been singled out as the method of choice for the evaluation of mutagenicity assay data, although a number of reports on statistical methods to evaluate such data have been published. Among the mutagenicity assays, the micronucleus assay using mouse bone marrow erythropoietic cells have been widely used to assess cytogenetic activities of test chemicals. A statistical evaluation procedure for this assay is proposed herein, combining the use of historical control data and dose-response relationships. The probability of type I errors and the power of this method are compared with those of some other conventional methods by Monte Carlo simulation.