Patients with symptoms that doctors cannot explain by physical disease are common in primary care. That they receive disproportionate amounts of physical intervention, which is largely ineffective and sometimes iatrogenic, is usually attributed to patients' belief that they are physically diseased, their denial of psychological difficulties, and their demand for physical intervention. The evidence for this view has mainly been doctors' subjective reports. By observing what patients and doctors say in consultation, we tested hypotheses arising from recent qualitative evidence. In particular, that physical intervention is proposed more often by general practitioners (GPs) than by patients, that most patients indicate psychosocial needs, and that GPs offer little effective explanation or empathy. Consultations of 420 consecutive patients identified by British GPs as presenting medically unexplained symptoms (MUS) were audio-recorded, transcribed and coded, utterance-by-utterance, using a specially developed coding scheme based on the previous qualitative analyses of these kinds of consultation. Physical intervention was, as predicted, proposed more often by GPs than patients. Also as predicted, almost all patients provided cues concerning psychosocial difficulties or their need for explanation. Although, contrary to prediction, most GPs did provide explanations other than physical disease, most also suggested physical disease. Few GPs empathised. The findings suggest that the explanation for the high level of physical intervention for MUS lies in GPs' responses rather than patients' demands, and we propose that explanations for 'somatisation' should be sought in doctor-patient interaction rather than in patients' psychopathology.