The effect of Al2O3 substitution on the acid durability of a Li2O-ZnO-SiO2 glass and its glass-ceramic was investigated depending on the applied heat treatments, the type and concentrations of acid solutions, and leaching time. Satisfactory acid durability was obtained by using 6 wt.% Al2O3 for the glass and 11 wt.% for the glass-ceramic. The acid resistance of both glasses and glass-ceramics was found to be affected markedly by the presence Of P2O5 or TiO2 used as nucleating agent. (C) 2002 Elsevier Science Ltd and Techna S.r.l. All rights reserved.