Object : The aim of this study was to examine an association between plasma 5-Hydroxyindoleacetic Acid(HIAA) level and the change of depressive symptom after fluoxetine trial in haloperidol-stabilized schizoprenic in-patients. Method : According to plasma 5-HIM level, 32 patients were classified to either group with high 5-HIAA level(N=11) or that with low 5-HIM(N=11). For each patient, fluoxetine(20mg/day) added to stable haloperidol dose for 6 weeks. The authors measured Hamilton Rating Scale for Depression (HRSD) at baseline, the 2nd week, the 4th week, the 6th week of treatment. Result : 1) Age, duration of illness, number of admission, duration of present admission, dosage of haloperidol between high 5-HIAA group and low 5-HIM group were significantly different. 2) As time went on, the association between the change of depressive symptom and plasma 5-HIAA concentration was not significant. 3) Of depressed group, as lime went an, depressive symptoms were improved significantly in high 5-HIAA group, but not in law 5-HIM group. Conclusion : We suggest that the association between plasma 5-HIAA level and the change of depressive symptoms after fluoxetine trial in haloperidol stabilized schizophrenic in-patients was not significant.