Atopic dermatitis (AD) is a common chronic or chronically relapsing, severely pruritic, eczematous skin disease. Recently, substance P (SP) has been demonstrated to be one of the important neuropeptides for mediating itch-scratch and stress-scratch cycles. In this study, we examined the severity scores, itch scores and plasma SP levels in 19 patients with AD treated with standard topical therapy with or without an oral antihistamine, olopatadine hydrochloride, for 4 weeks. The standard therapy decreased SCORAD scores, itch behavioral rating scores and plasma SP levels at post-treatment in the mass, but the topical therapy with olopatadine was more effective than the topical therapy alone, suggesting a potential additive effect.