Alterations in vascularisation, vasodilatation and tissue osmotic pressure (OP) are inevitable aspects of the inflammatory process that have an adverse effect on the fluid dynamics of the tissue involved. The aim of this study was to investigate tissue OP and its relationship with the vasculature in inflammed gingival tissues, in order to reveal the possible effects of vascular changes on OP in the fluid dynamics of periodontal soft tissues during periodontal disease. The parameters of fluid dynamics assessed in this study were OP, vascularisation and vasodilatation. Ligature-induced periodontitis was performed in 10 rats (test group), and gingival biopsies taken from the diseased teeth were utilised for the test procedures. These biopsies were compared with biopsies of the same teeth from 10 periodontally healthy rats (control group). OP was measured in mosmol/kg using a semi-micro digital osmometer. Vascularisation and vasodilatation were examined histopathologically; the number of vessels (VN) was quantified and the micrometric changes in vessel diameters (VD) were calculated as the alterations in the vasculature. OP, VN and VD were found to be higher in the test group (84.3 ± 37.1 mosmol/kg, 13.2 ± 3.2 and 19.5 ± 1.3 μm, respectively) than the control group (11.6 ± 3.8 mosmol/kg, 6.8 ± 1.1 and 15.5 ± 2.4 μm, respectively) (P < 0.000). There was a strong, positive correlation between OP and VN (r = 0.55, P < 0.000) and a weak, negative correlation between OP and VD (r = 0.1, P > 0.05) in the test group. These results confirm that the OP of periodontal soft tissues does change during inflammatory conditions. The increase in OP during this process may be affected by increased vascularisation in the inflammed tissue. © 2005 Elsevier Ltd. All rights reserved.