We examine the conditions for trust relationships between patients and physicians. A trust relationship is not normally negotiated explicitly, but we wanted to discuss it with both patients and physicians. We therefore relied on a combination of interviews and observations. Sixteen patients and 8 family physicians in Norway participated in the study. We found that trust relationships were negotiated implicitly. Physicians were authorized by patients to exercise their judgment as medical doctors to varying degrees. We called this phenomenon the patient's mandate of trust to the physician. A mandate of trust limited to specific complaints was adequate for many medical procedures, but more open mandates of trust seemed necessary to ensure effective and humane treatment for patients with more complex and diffuse illnesses. More open mandates of trust were given if the physician showed an early interest in the patient, was sensitive, gave time, built alliances, or bracketed normal behavior.