A quartz crystal microbalance apparatus has been assembled to measure the diffusivity and solubility of penetrants in polymers. The first system studied to test the validity of the results was poly(vinyl acetate)-toluene at 40°C. A toluene vapor pressure of 10.5 torr was exposed to the polymer sample, which had a thickness of 201 nm. The feasibility of measuring mass uptake was demonstrated with the first experiment. The results, however, showed unexpected behavior and did not agree fully with literature data. The source of the discrepancy will require further investigation.