A study was undertaken to compare the efficacy of a soaking solution (Efferdent Extra-Strength Denture Cleanser Tablets) to mechanical cleaning with a denture paste (Advanced Formula Dentu-Creme Denture Cleaning Paste) to remove and kill plaque bacteria from removable dentures. The study was conducted in a randomized, four-way crossover fashion with 18 subjects. At each clinic visit, subjects were randomized to one of four treatment regimens: 1) no treatment; 2) brushing with denture paste; 3) soaking in Efferdent; 4) brushing followed by soaking in Efferdent. Microbiological sampling for plaque bacteria was made before and after each treatment. Aliquot samples of 10-fold serial dilutions were plated on supplemented Schaedler Agar (for total anaerobes) and on CVE agar (for fusobacteria). Analysis of covariance was performed on the log10 transformed scores at posttreatment using the pre-treatment scores as covariates. Significant treatment effects were: F(3,41) = 81.60, p less than 0.001 for anaerobes and F(3,50) = 104.38, p less than 0.001 for fusobacteria. Pairwise comparisons using Tukey hsd post hoc tests showed that for total anaerobes, treatments 1 and 2 yielded higher scores than treatments 3 and 4. For fusobacteria, treatment 1 greater than 2 greater than 3 or 4; no difference between treatments 3 and 4. The results demonstrated the superior performance of Efferdent over Dentu-Creme.