A microcomputer controlled microindenter with a flat cylindrical microindenter face has been used to measure the variation of storage modulus and loss factor that results from differences in microstructure in high density polyethylene (HDPE). The microstructural variations have been produced by butt welding the polyethylene and varying the thermal histories of the weld. The dynamic mechanical thermal analysis data from the microindenter have been compared to similar tests on uniform bulk material run in bending using a commercial analyzer. The normalization procedure used on the microindenter data was justified by examining the calculated stress fields under the indenter tip. The quantities measured using the microindenter are consistent viiith the measured changes in crystallinity.