Purpose: The aim of this study was to compare the residual monomer and microhardness of poly(methyl methacrylate) (PMMA)-based denture resins processed by using autoclave and conventional water bath techniques.,Methods: To determine the amount of residual methyl methacrylate (MMA) monomer, disk-shaped specimens (n=5) were prepared from 3 different acrylic resins (Meliodent, Paladent and Qc-20). Control groups were polymerized in water bath for 30 minutes at 100 degrees C. The study groups were prepared in an autoclave device for 60 degrees C/30 min followed 130 degrees C/10 min and the other group for 60 degrees C/30 min followed by 130 degrees C/20 min. According to standard calibration curves, ultraviolet spectrophotometry at 230 nm was used to determine the residual monomer. For the Vickers hardness measurements, disk-shaped specimens (n=5) were prepared for each test group. Hardness measurements were performed with a Vickers hardness tester under a 4.91-N press load for a 30 seconds, after immersion in distilled water at 37 degrees C for 48 hours. The data were analyzed by ANOVA and Tukey HSD test (p<0.05).,Results: Autoclave polymerization produced a significant decrease in the amount of residual monomers for all resin groups (p<0.05). This procedure also showed a significant increase in hardness for all resin groups (p<0.05). For the 3 resin groups, no significant differences were found between autoclave polymerization for 10 minutes and for 20 minutes (p>0.05).,Conclusions: The autoclave polymerization technique exhibited significantly lower residual monomer content and greater hardness than conventional heat polymerization.