A Delphi technique was used to ask general practitioners for their opinions as to which clinical problems and types of measure they thought most appropriate for the development of outcome measures for use in primary health care. The study comprised two rounds of postal questionnaires, targeted at general practitioners in academic departments throughout the United Kingdom and at trainers in the northern region, with the second questionnaire feeding back opinions from the first. Ninety eight participants suggested one or more areas in which outcome measures could be developed, giving a total of 451 suggestions. Consensus produced in the second round indicated that three clinical conditions were preferred for the development of outcome measures: asthma, diabetes and hypertension. Six categories of outcome measures were developed from the responses given in the first round--level of function, level of clinical control, incidence of complications, iatrogenic problems, patient understanding of a condition, and quality of life. Participants gave these measures different levels of importance according to the clinical problem in question. This Delphi study of doctors' opinions is a first step in the development process of appropriate, practicable measures of outcome for use in primary care and has achieved a degree of consensus among general practitioners.