Despite the fact that knowledge spillovers have explicitly geographic components, the role of spatial effects in the knowledge spillover process has been ignored. In this context, the objective of this paper is to observe differences in the spatial distribution of innovative activity across U.S. metropolitan areas, and thereby to examine whether the concentration of innovative activity in a metropolitan area is spatially correlated to the concentration of neighboring metropolitan areas’ innovative activity. Based on a data set of patents, this paper presents the recent space-time patterns of metropolitan innovative activity for the period 1990-1999.