Gingival crevicular fluid (GCF) is a promising source for markers of destructive periodontal diseases activity. As the initial stage of a longitudinal study into the characterization of disease markers, GCF sampled from 104 sites in 74 adolescents was examined via sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS/PAGE). In this population, which had varying degrees of gingivitis but little evidence of destructive periodontitis, there was a highly homologous GCF protein profile. The plasma components, albumin, transferrin and IgG, were major constituents of all samples. In addition, a second group of non-plasma derived proteins, with molecular weights 37 kDa, 47 kDa, 57 kDa and 59 kDa, was also commonly detected. The high frequency of occurrence of these components suggests that they may represent products of normal turnover of the periodontal tissues. Analysis of GCF sampled from patients with progressing destructive disease revealed a different SDS/PAGE profile particularly with respect to proteins of non-plasma origin. It is anticipated that the major metabolic changes which accompany the destruction of the tissues during future disease episodes in the adolescent study population will be discernible as alterations to the GCF protein profile.