Samples of gingival fluid and plasma were taken from ten patients with varying severity of periodontal disease. Group I comprised seven patients with abundant plaque. Their mean pocket depth at the sampling sites was 5.6 ± 1.27 mm. Group II consisted of three patients with minimal plaque and a mean pocket depth of 1.8 ± 0.24 mm. A comparative analysis by crossed immunoelectrophoresis was carried out. Qualitatively evaluated orosomucoid and the complement factor C3 were degraded in all the gingival fluid samples, in contrast to those of plasma. A quantitative assay of 15 separate proteins in the two biological fluids showed reduced concentrations of alfa1‐antichymotrypsin, alfa2‐macroglobulin and haptoglobin in most gingival fluids. Orosomucoid, alfa1‐antitrypsin and C3 levels were decreased in all the gingival fluid samples. Reference ranges should be stated separately for the two biological fluids. The correlation coefficients between the plasma and the gingival fluid concentrations of each protein were calculated. The co‐variation was significant for 13 of the proteins studied. The ratio of the individual protein concentrations in the gingival fluid to that in the plasma was then calculated for each patient. A twoway analysis of variance of the variables patient groups and protein ratios showed that both effects were significant. Gingival fluid is an inflammatory exudate of serumal origin, but its protein profile is clearly modified by the loc