Two issues that arise in the design and statistical analysis of in vivo SCE and similar experiments are considered. First, with regard to analysis, the merits of various methods of data transformation are explored in depth. The conclusion drawn is that common transformations of the type studied here seemingly offer little advantage in the assessment of whether a test agent induces SCE in a dose-related manner. Second, a proposal is made for a method to determine, subject to budgetary constraints, the desired numbers of animals/dose group and cells scored/animal. The approach advocated also lends itself to discussions weighing the gains and losses from possible reductions in the number of animals below the 'desired' levels.