The purpose of this study was to observe the effect of immersion in water at 3, 5, 7, and 10 minutes after mixing on the surface of three regular and one light-curing glass-ionomer cements by measuring penetration of a methylene blue solution. Early solubility of these cements was also measured and compared with that of a zinc phosphate and a polycarboxylate cement. A blue-stained zone was observed in all glass-ionomer cements, but an inner, opaque zone was observed in only two of the regular glass-ionomer cements. Extending the time between start of mixing and immersion in water decreased the width of both zones in all cements and markedly lowered the loss of substance from the surface of regular glass-ionomer cements. However, time after mixing had no or only a limited effect on the loss of substance from the light-curing glass-ionomer cement, the zinc phosphate cement, or the polycarboxylate cement.