There have been no previous reports in the literature comparing the effects of hand scaling with ultrasonic debridement in furcations, or which have used dark-field microscopy for this comparison. The purpose of this study was to compare the efficacy of these two modes of debridement in various classes of furcations, using gingival crevicular fluid flow and dark-field microscopy as parameters. A total of 33 furcated molars were evaluated. Results indicated that both hand scaling and ultrasonic debridement were equally effective in Class I furcations in changing the gingival fluid flow and bacterial proportions to those of a healthy state. In contrast, ultrasonic debridement was significantly more effective than hand scaling in Class II and Class III furcations in altering these parameters.