Objective To study the spatial distribution character of brain evoked potential(BEP)in primary depressive illness(PDI)patients and the effect of Yi'nao Jieyu Formula.Methods Case control study and self-control study in Chinese herbal treatment group were conducted.Brain-stem auditory evoked potential(BAEP)and visual evoked potential(VEP)of 60 PDI patients and 45 healthy controllers were recorded by BEP apparatus made in Italy.BAEP and VEP of 30 patients of PDI group were detected again after taking Yi'nao Jieyu Formula for 6 weeks.Results Latencies of whole waves in BAEP and VEP prolonged significantly in PDI group(P