ABSTRACTRecent attempts to broaden the scope of spatial interaction models have focused on introducing elements of competitive market structure. These extensions advance our understanding of spatial markets, but fail to deal adequately with forms of impedance other than distance. These limitations are critical when dealing with different types of interaction. Business services, in particular, are less sensitive to distance as a source of impedance. In this paper, we introduce an approach to model the trade of business services that extends upon traditional models of spatial interaction. We propose a model of trade that defects competitive market stuctures and differentiates the traditional spatial source of impedance from an aspatial source. The model is evaluated with sales data obtained from a survey of business service firms in the Chicago metropolitan region.