This paper examines conceptions of trust among three groups of respondents diagnosed with either breast cancer, Lyme disease or mental illness. Interviews were carried out using an open-ended interview guide to explore how patients made assessments of trust in their doctors and health care plans. The guide followed a conceptual approach that asked questions about competence, agency/fiduciary responsibility, control, disclosure and confidentiality. Respondents were given ample opportunity to raise other areas of concern. The data were organized using the NUDIST software package for the analysis of non-numerical and unstructured qualitative data. Patients viewed trust as an iterative process and commonly tested their physicians against their knowledge and expectations. Interpersonal competence, involving caring, concern and compassion, was the most common aspect of trust reported, with listening as a central focus. Most patient comments referred to learnable skills and not simply to personality characteristics. Technical competence also received high priority but was often assessed by reputation or interpersonal cues. Patients were much concerned that doctors be their agents and fight for their interests with health care plans. Disclosure and confidentiality were less common concerns; most patients anticipated that doctors would be honest with them and respect their confidences. Patients' responses also appeared to vary by their disease, their socio-demographic characteristics, their involvement with self-help groups, and how their illness conditions unfolded.