The in vivo solubility of glass-ionomer, zinc polycarboxylate, and zinc phosphate luting cements was compared. The specimens were inserted in the lingual flanges of the mandibular dentuers of 10 edentulous patients. After 8 months, the cement specimens were removed and the amount of solubility was measured with direct techniques. Scanning electron microscopy was used to evaluate surface topography after disintegration. The elements present in each cement were determined with energy-dispersive spectroscopy. The zinc phosphate and zinc polycarboxylate cements demonstrated approximately equal solubility. Glass-ionomer cement exhibited significantly less solubility than did either zinc phosphate or poly-carboxylate cement.