The paper aims first to analyse the presence of knowledge in innovative firms located in industrial districts (ID) in order to compare with similar non-district (NID) firms. This approach assumes the presence of an industrial district effect, i.e., the presumption of a better performance of knowledge and economic results in the first group of firms. We also try to identify the existence of an interdistrict effect, i.e., the emergence of gaps in the knowledge of ID innovative firms of different technological intensity. In both cases we focuse on Valencian ID in Spain. We introduce the idea of innovative firms (IF) as a unit of analysis on the assumption that: a) they reflect superior use of knowledge resources as inputs for business innovation generation; and b) their greater use of these resources facilitates the absorption of knowledge spillovers flowing through the district. The empirical analysis uses an original database containing information on 5,553 innovative companies in the region. The mean analysis applied allows us to identify variables with statistically significant differences as a preliminary to isolating groups of firms with more pronounced central values. The results show the presence of differences characterizing companies with different levels of innovation in ID and NID, as well as the groups of innovative firms belonging to districts with differing technological levels. In the first case, the superiority of innovative companies does not emerge, consequently, we cannot confirm the existence of a district effect. However, we can detect some evidence of an inter-industry effect in the performance of innovation firms in footwear, textiles and ceramics.