The presence and levels of complement factors C3, C4, C5, and C3 proactivator, were determined by electroimmuno assay in gingival cervice material from five individuals with healthy gingiva and from six patients with chronically inflamed gingiva. Higher concentrations of C3 and C4 were found in samples from chronically inflamed gingiva when compared to those healthy gingiva. The amount of C3 in material from healthy as well as from inflamed gingiva was related to that in plasma, when the albumin in plasma and gingival crevice material was used as a reference. The same was found for C4 in samples from healthy gingiva but in those from inflamed gingiva, the values were significantly lower when related to plasma levels. C5 could not be found in material from healthy gingiva but was present in material from inflamed gingiva. C3 proactivator was present in material from inflamed gingiva in the converted form. No C3 proactivator was found in material from healthy gingiva with the methods used. Analysis of C3 in samples from inflamed gingiva, using crossed immunoelectrophoresis, showed that C3 was converted in these samples. The results indicate that the complement system may be activated in gingival crevice material from inflamed gingiva.