Soft tissue injury is accompanied by lowering of interstitial fluid pressure (P_if), plasma protein extravasation, and edema. Inflammation was produced by electrical stimulation (ES) of the vagus and the effects of the synthetic peptide mystixin-7 (p-anisoyl-Arg-Lys-Leu-Leu-D-Thi-Ile-D-Leu-NH₂) on P_if were examined. Micropuncture measurement of P_if in submucosa, without opening the trachea, was conducted on rats anesthetized with pentobarbital sodium (50 mg/kg) and euthanized with intravenous KCl. P_if in control (intravenous saline) was 1.2 ± 0.7 mmHg before ES and decreased to 4.7 ± 1.0 mmHg (P < 0.01, n = 8) after ES. Mystixin-7 (10 and 20 µg/kg iv) blocked the fall in P_if after ES (1.1 ± 0.3 and 0.8 ± 0.2 mmHg, P < 0.01, n = 8 and n = 4). The 1 µg/kg dose was without effect. When trachea from animals pretreated with mystixin-7 (20 µg/kg iv) were soaked in phosphate-buffered saline (0.15 M, pH 7.4), the rate of fluid accumulation was significantly reduced. This study suggests that mystixin peptides, which have structural similarity to a fragment from laminin-1 chain, may be useful tools for studying cell adhesion and factors that maintain the structural integrity of connective tissue after injury.