In a previously published study on the effect of an alcalase on development of denture plaque, two different methods were used to quantify plaque on the fitting surface of maxillary dentures. Both methods were based on scoring of photographs at×10 magnification. In one of the methods the percentage area was estimated with 10% intervals from 0% to 100%. By the other method dentures were ranked according to cleanliness based on area and on degree of staining of plaque. The number of dentures in each of the 14 treatment periods was 14 or 15. The present study was conducted to determine the reliability of the two methods. Reliability of the two methods was determined by using Pearson's correlation coefficient and Kendall's tau. Both intra- and inter-examiner reliability was high. A high correlation between the two methods was also demonstrated.