•Contributes to the understanding of how fast growth of entrepreneurial science-based firms occurs.•Conceptualizes the speed of early growth as the time it takes for the assembly of three types of critical resources—a functionally-diverse management team, early fundraising and development of technology.•Distinguishes between “assisted” and “unassisted” paths to access critical resources, and how they combine to influence the speed of early firm growth.•Shows how manifestations of technology development act as signaling devices to attract funding and management, affecting the speed of firm growth.•Shows how the variety of paths and speed of early growth is influenced by the national institutional setting. The paper explores the process of early growth of entrepreneurial science-based firms. Drawing on case studies of British and Dutch biopharmaceutical R&D firms, we conceptualize the speed of early growth of science-based firms as the time it takes for the assembly (or combined development) of three types of critical resources—a functionally-diverse management team, early fundraising and development of technology. The development of these resources is an unfolding and interrelated process, the causal direction of which is highly ambiguous. We show the variety of paths used by science-based firms to access and develop these critical resources. The picture that emerges is that the various combinations of what we call “assisted” and “unassisted” paths combine to influence the speed of firm growth. We show how a wide range of manifestations of technology development act as signaling devices to attract funding and management, affecting the speed of firm development. We also show how the variety of paths and the speed of development are influenced by the national institutional setting.