In an age of flattened hierarchies and networked organizations, lateral processes in organizations take on added significance. Co-worker assistance refers to a key aspect of lateral relations: workers’ helping behaviour in relation to their immediate colleagues. Using data from a Dutch survey of public sector and related service employees, we develop and test a model of co-worker assistance. We argue that reciprocity facilitates management-induced co-worker assistance and that this depends on the extent of workers’ organizational commitment. This in turn is influenced by the manner in which management exercises control over employees. We find evidence for organizational commitment acting as a partial mediator between co-worker ssistance and bureaucratic control, co-worker control, and facilitative supervision respectively. Group cohesion, forged by workers independent of management, has a strong direct effect on co-worker assistance and a particularly strong effect when interacting with co-worker control. We also find that co-worker control is more strongly related to co-worker assistance where tasks are more interdependent.