The levels of prostaglandin E2 (PGE2) and interleukin-1 beta (IL-1 beta) were determined in gingival crevicular fluid (GCF) collected from patients with gingivitis: 15 Down syndrome children and 15 controls. The mean level of PGE2 in GCF was significantly higher (P < 0.05) in the Down syndrome group (10.0 pg/microliters GCF) than in the control group (4.6 pg/microliters GCF). In GCF samples collected from sites characterized as noninflamed, the mean level of PGE2 was significantly higher (P < 0.001) in the Down syndrome group than in the controls. The mean level of PGE2 in samples from inflamed sites, on the other hand, did not differ between the two groups. The mean level of IL-1 beta was not significantly higher in the Down syndrome group than in the controls. This study shows that the level of PGE2 detected in GCF from Down syndrome patients is increased, a fact that may be of importance in the pathogenesis of the periodontal disease frequently seen in these patients.