The paper addresses the role played by research-based spin-off firms (RBSOs) as knowledge dissemination mechanisms, through their position in knowledge networks. Previous research found that, despite the continued relevance of links with research organisations, these firms frequently play an intermediary role between academia and industry, and started characterising the forms assumed by that role (Conceicao, Sousa and Fontes, 2017; 2018). This paper extends this approach by proposing that the composition and structure of the knowledge networks and the position occupied by RBSOs are not homogeneous, but vary between industries, being associated with the nature of the knowledge prevalent in that industry. For this purpose, the paper draws on the notion that innovation process in firms and industries are strongly shaped by their specific "modes of knowledge creation" or "knowledge bases", which have been categorised as analytical, synthetic or symbolic (Asheim and Coenen, 2005). According to the literature these modes of knowledge creation influence the nature of interactions that take place (Moodysson et al, 2008; Plum and Hassink, 2011; Salavisa et al, 2012) and, therefore, they are expected to introduce some differentiation in the knowledge networking behaviour of the RBSOs. The empirical research is based on the data on the publicly funded collaborative research and technology development projects established by the population of RBSO created in Portugal until 2007, encompassing both domestic projects, funded by national programmes (237 projects) and international projects, funded by European Framework Programmes (216 projects) and covering a broad spectrum of industries. The industries were classified according to their knowledge bases. The knowledge networks, associated with the participation of RBSO in those projects, were (re)constructed and analysed using a set of measures from social network analysis, with a view to uncover and assess their composition and structure. The results show that, despite RBSOs common academic origin, there some differences in the structure of the knowledge networks of firms in different industries, in particular between those characterised by an analytical knowledge base (of which biotechnology emerges as the most paradigmatic case) and a synthetic knowledge base. These differences have implications for position and role of RBSOs in the networks.