Gingival fluid was collected with glass capillaries tubing from the upper premolar area in a group of 7 volunteers, after allowing dental plaque to accumulate for 12-36 h, and in a group of patients with gingivitis. Whereas no fluid could be collected in the absence of plaque, increasing amounts were recovered during plaque accumulation, in the absence of clinical signs of gingival inflammation. The ratios of albumin concentrations in gingival fluid and plasma also increased significantly with increasing time of plaque accumulation. These fluid:plasma ratios of albumin concentrations were significantly lower than the ratios found for the inflamed sites in the second group of patients. These results support the hypothesis that, in an early inflammatory response, the fluid is not a typical inflammatory exudate and is probably modulated by an osmotic gradient.