The excess prescribing of mood-modifying drugs to women has been observed for some time, but the explanation for the sex difference has resisted analysis. In this paper, we develop five distinct hypotheses which summarise several of the most popular explanations and subject them to empirical test using data collected independently from doctors and patients in 1301 general practice consultations. The survey was conducted in Sydney, Australia in 1976, and includes information on psychiatric morbidity, presenting complaint, diagnosis, and prescription. Cross-tabular and regression analyses suggest that higher rates of consulting by women and perhaps a higher incidence of female morbidity account for much of the prescribing differential. That is, the main sources of the sex difference in prescribing appear to lieoutside the consultation rather than arising from doctor/patient interaction. The one exception to this is that doctors tend to underdiagnose psychiatric disturbance in males.