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Titanium doping has been successfully employed to increase high field Jc in internal tin (IT) type conductors. Titanium doping is achieved by placing Nb-47Ti rods within the filament array. Doping occurs during reaction heat treatment as a result of titanium diffusing from the Nb-47Ti source into the niobium filaments. We have investigated doping of internal-tin-tube (ITT) type conductors using Nb-47Ti rods placed in holes drilled into the niobium annulus of each filament. The titanium distribution at various stages during reaction heat treatment was investigated by SEM/EDS and the A15 grain boundaries were examined with Scanning Auger Microanalysis. We observed that there is minimal titanium diffusion into the niobium until the Nb3Sn reaction front reaches the Nb-47Ti source, and that there is a loss of titanium to the residual filament core and the core/annulus interface. It was determined that the primary route for titanium diffusion is through the A15 grain boundaries.