The impact of firm size on innovation activity was investigated in detail on the basis of firm data for Swiss manufacturing. The study includes estimations of a model of innovation behavior with firm size as an additional explanatory variable, an analysis of the relation between R&D expenditures and firm size in total manufacturing and in several 2-digit industries, as well as exploration of the size-dependence of model variables. No evidence was found for the existence of economies of scale in the innovation activity in Swiss manufacturing. On the other hand, we were able to gather several pieces of information pointing to a size-specific orientation of the innovative activity. Copyright 1997 by Kluwer Academic Publishers