This article explores the complexities of James Petiver and Hans Sloane's relationship with one another and their shared contacts, examining the ways in which their networks overlapped but also, crucially, differed from one another. It shows that, though they had common interests and institutional memberships, Petiver ultimately occupied a different urban world from Sloane, a middling, trade-orientated stratum of society with its own forms of sociability and business, credit and advancement. It was this position that helped Petiver bridge a range of gaps in elite scholarly exchange, making himself indispensable through his effective mediation between different urban groups and access to spaces beyond Sloane's reach. It argues that greater attention needs to be paid to the imbrication of middling interests and agencies that operated across London's natural history communities, in order to prompt us to think more carefully about the strategies and interests of those who tried to navigate them.