A computer programme (DPAX) was constructed for a longitudinal study of psychiatric epidemiology in Stirling County (Canada). It identifies disorders involving the syndromes of depression and anxiety based on responses given in structured questionnaire interviews. The programme follows a diagnostic algorithm that uses criteria for: (1) essential features; (2) number, frequency, and pattern of associated symptoms; (3) impairment; and (4) duration. The programme reproduces case evaluations provided by psychiatrists, as conveyed by a sensitivity of 92% and a specificity of 98%.