Poly(methyl methacrylate) dentures may exhibit dimensional changes when drying. Drying has been shown to destroy Candida albicans. This study investigates the effect of simulating overnight cyclic drying on dimensional changes of four complete denture base materials. Denture specimens used in this study had been prepared for a previous study. All dentures had been kept hydrated at room temperature for 2 years. The materials used were, group 1, conventionally packed and cured Trevalon, group 2 was injection moulded and conventionally cured (Trevalon Success), group 3 (Acron MC) and group 4 was Microbase, which is injection moulded and microwave cured. The measurements of the inter-molar and inter-premolar width, and anterior posterior dimension between the premolars and molars were recorded after 8 h drying and then after four cycles of dehydration and rehydration. The dentures were more dimensionally stable in the anterior posterior than the cross arch dimension. There was a statistically significant (P < 0·02) increase in the intermolar width for Trevalon, Trevalon Success and Acron after 8 h drying and after four cycles. There was a statistically significantly difference between Microbase and the other materials after 8 h drying and there was a significant difference between the injection moulded groups in the interpremolar width (Trevalon Success versus Acron, Trevalon Success versus Microbase) after cyclic drying. Although statistically significant dimensional changes were observed for all materials these were small and were considered not to be clinically significant. Microbase was the least dimensionally stable material during air-drying.