A study of the linearity of a digital microbalance was made to determine microbalance performance with high crystal loading. The 5-MHz crystals were loaded by 30Å/sec deposition of Al in 40 kÅ steps and Cu in 8 kÅ steps. The film thickness, measured on an adjacent quartz, optical flat, was compared with the indicated film thickness of the microbalance (computed from crystal period shift). The data presented, which show linearity within ±0.3%, agrees with a theory that postulates no elastic loss within the deposited film. However, a transient phenomenon is observed with both Al and Cu that could result in microbalance errors of greater than 5%. Deposits of up to 25 mg/cm2 (950 kÅ of Al) were studied to evaluate the magnitude of this potential error.