A comprehensive structured psychiatric interview suitable for use by nonphysicians is described and its reliability evaluated. The schedule, called the Home Environment and Lifetime Psychiatric Evaluation Record (HELPER), includes extensive social background data, assessment of home environmental factors, and all items necessary for psychiatric diagnoses using several available sets of operational criteria. This schedule emphasizes the lifetime chronology of events and includes more detailed assessment of nonaffective symptomatology and social environmental background than other available instruments. Thirty-four psychiatric inpatients were assessed by physicians and nonphysicians using an interviewer/observer design. Inter-rater agreement for psychiatric symptoms and 11 possible syndromes was substantial (mean K 0.70 and 0.72, respectively) and for home environmental experience it was excellent (mean K 0.88). Nonphysician interviewers made ratings comparable to those of physicians even for those items thought to require the most clinical and medical judgment. The reliability and usefulness of nonphysician interviewers as part of a research team are demonstrated by these findings. More extensive application of structured psychiatric interviewing is encouraged.