Few studies have investigated directly the possible role of dietary sugar in the etiology of periodontal disease, although an association between the amount of plaque formed and the frequency of sugar intake has been demonstrated. The purpose of this study was to examine the influence of frequent sugar intakes on experimental gingivitis in young adults. Twenty male dental students took part in a single blind crossover study which involved two 3-week experimental periods with random allocation to high or low sugar diets. The experimental site was the lower anterior area. The labial aspects of the lower anterior teeth were examined at baseline and Weeks 1, 2 and 3. Inflammation was assessed by recording bleeding on probing at 12 sites at 2 levels of severity--"pin prick" and "excess." In addition gingival crevicular fluid flow was recorded and plaque amount was assessed. At 3 weeks significantly higher bleeding scores at the two designated levels were found with the high sugar diet but no significant differences were observed with crevicular fluid flow and plaque amount. It was concluded that frequent sugar intakes result in increased gingival inflammation in experimental gingivitis, as measured by gingival bleeding on probing.