In situ and ex situ quartz crystal microbalance measurements were made at a 10 MHz AT-cut piezoelectric resonator. A simple test is described to determine whether immersion in a solvent affects the relationship between mass loading and frequency decrease found in air. For mass loadings produced with electrodeposited silver up to 400 mu g cm(-2), the resonant frequencies in air and in aqueous solution were found to be linearly proportional to each other with a slope of unity at the 5% significance level.