The effects of 2,5-dihydroxybenzene-1,4-disulphonic acid-bisdiethylamine salt (263-E) and trihydroxyethylrutoside (Vitamin P4) on capillary permeability have been compared in the rabbit. Both drugs were administered by intradermal and intravenous routes. Histamine and bradykinin were injected intradermally to increase permeability. 263-E was sown to be a potent inhibitor of permeability changes induced by histamine and bradykinin intravenous routes. Vitamin P4 maximally inhibited permeability at the lowest intravenous dose level but with increasing dose the inhibition became negligible. After intradernal administration, vitamin P4 did not inhibit permeability but potentiated the permeability response induced by histamine and bradykinin.