The properties of denture base and reline resins may be affected by daily changes between room temperature and mouth temperature. The purpose of the study was to evaluate the effect of thermocycling on the flexural strength of the relined denture base polymer with reline resin. Three denture base resins, three hard reline resins and their combinations were tested. Fourteen specimens, 65x10x2.5 mm, were fabricated for each material. Polymer combination specimens were made using 1.5 mm hard reline resin on 1.0 mm cured denture base resins. Half of the specimens were stored for 50+/-2 h in distilled water at 37 degrees C, while the other half were thermocycled for 20 000 cycles between 4 and 60 degrees C. Three point bending tests were conducted on a universal testing machine at a cross-head speed of 0.5 cm/s. The flexural strengths were measured and a statistical analysis was performed on the data using three-way ANOVA (P<0.05). The results showed that the flexural strength of relined denture base polymer was significantly higher than that of hard reline polymer. Thermocycling did not affect the flexural strength of the relined denture base polymers, whereas the denture base polymer and reline polymer alone showed a decrease in strength after thermocycling.