Manganese is essential to human life for normal neurological and skeletal functions. Longstanding, excessive exposure to Mn compounds may result in manganism, a Parkinson's disease like syndrome. Prolonged exposure to Mn at low levels can result in memory deficit, loss of motor control and reduction in the refinement of certain bodily motions. A feasibility study of measuring Mn concentrations in human bone with in vivo neutron activation analysis (IVNAA) was previously reported.1 Since then, an irradiation/shielding cavity, consisting of moderator, gamma-ray filter, neutron reflector, and shield walls, was constructed for the clinical application of Mn IVNAA,2 and an upgraded IVNAA system is reported here. The minimum detectable limit is 0.081 mg in the hand, which is toward the lower end of the estimated bone Mn level of 0.065 to 1 mg in the hand of healthy subjects. A significantly lower radiation dose is delivered than in the reported feasibility study.