The complementarities between internal capabilities and external linkages have been widely acknowledged in the open innovation literature, yet little is known about the extent to which internal capabilities affect firms' openness within different institutional contexts. This paper therefore empirically explores the relationship between absorptive capacity (ACAP) and openness in the United States and European biopharmaceutical sectors. Based on analysis of data from a large-scale international survey of 349 biopharmaceutical firms in the United States, the United Kingdom, France and Germany, the results suggest that exploratory openness depends more strongly on the research and development (R&D) aspect of firms' potential absorptive capacity, whereas exploitative openness is more conditional on firms' realized absorptive capacity (RACAP). The results also highlight the major differences between firms' openness and ACAP in the United States and Europe - in the United States, firms' skill levels prove more significant in contributing to firms' engagement with exploratory relationships, whereas in Europe, continuity of R&D proves more important. Engagement with exploitative relationships, however, is more conditional on firms' RACAP in Europe only.