In this paper, we explore the effect of residual hip assistance in one above-knee amputee subject using a novel lightweight powered hip exoskeleton. Differently from a powered prosthesis, a powered hip exoskeleton adds mass proximally. Thus, we expect that the negative effect of the added mass will be lower for a powered hip exoskeleton than a powered ankle and knee prosthesis. Consequently, residual-hip assistance may more easily lead to a net reduction of metabolic effort. To preliminarily assess this hypothesis, we measured the physiological cost index (PCI) while an above-knee subject walked with and without a powered hip exoskeleton. Experimental results show 20.5% reduction of PCI when walking with the powered hip exoskeleton.