Microhardness was evaluated as an indicator of appropriate finishing intervals for glass ionomer restorative materials. The hardness of several materials was determined after the first hour of mixing. A material clinically documented to be satisfactorily finished after a delay of 15 minutes attained 29% of its 24-hour hardness during that interval. Samples of the other materials finished on reaching this relative hardness, which differed from the manufacturers' suggested finishing delays, showed no differences in surface characteristics, appearance, or surface roughness compared with specimens finished at the recommended times.