Technological solutions to problems of knowledge and practice in health care are routinely advocated. This paper explores the ways that new systems of practice are being deployed as intermediaries in interactions between clinicians and their patients. Central to this analysis is the apparent conflict between two important ways of organizing ideas about practice in primary care. First, a shift away from the medical objectification of the patient, towards patient-centred clinical practice in which patients' heterogeneous experiences and narratives of ill-health are qualitatively engaged and enrolled in decisions about the management of illness trajectories. Second the mobilization of evidence about large populations of experimental subjects revealed through an impetus towards evidence-based medicine, in which quantitative knowledge is engaged and enrolled to guide the management of illness, and is mediated through clinical guidelines. The tension between these two ways of organizing ideas about clinical practice is a strong one, but both impulses are embodied in new 'technological' solutions to the management of heterogeneity in the clinical encounter. Technological solutions themselves, we argue, embody and enact these tensions, but may also be opening up a new array of practices - technogovernance - in which the heterogeneous narratives of the patient-centred encounter can be resituated and guided.