Interim soft denture liners or conditioners may be valuable therapeutic materials. The life of these liners varies, but it can be extended by the use of a poly(methyl methacrylate) coating material (Monopoly). This study evaluated the ability of Monopoly to prevent water absorption and plasticizer loss from an underlying tissue conditioner (Visco-gel). Disk specimens of Visco-gel coated with Monopoly were immersed in water that was sampled at 24 hours, 1 week, 2 weeks, and 1 month. Uncoated Visco-gel samplea acted as controls. Water absorption was determined gravimetrically at each time interval and decanted water was subjected to separation by reversed phase high performance liquid chromatography for component identification. All samples suffered significant initial weight loss followed by a trend toward weight gain in the uncoated control group, probably because of water absorption. The Monopoly coating appeared to reduce this effect. Plasticizer loss from the tissue conditioner was below quantifiable limits by high-performance liquid chromatography, but methyl methacrylate monomer loss from the Monopoly coating was demonstrated. Some clinical implications are discussed.