Mood changes of interns during the internship year were studied using the Profile of Mood States (POMS), a standardized adjective checklist. All 35 interns in the University of California, Irvine-Long Beach Medical Program completed the POMS at internship orientation and at five other times during the year. Of the six mood factors measured by the POMS, four changed significantly during the testing period. Anger-hostility scores were higher (p<0.01) in December than at orientation and remained so throughout the year. Tension-anxiety scores were higher (p<0.01) and fatigue-inertia scores were lower (p<0.01) at orientation than at any other time during the year. Vigor-activity scores were higher (p<0.01) at orientation than at the end of the year. Depression-dejection and confusion-biwilderment scores did not change significantly during the study period. Recognition of these mood changes is helpful for drawing the attention of house staff and faculty members to emotional stresses of training, and for identifying issues for discussion in intern support groups.