A pressure-driven flux of water occurs across the arterial wall in vivo. We have investigated the role of several interstitial components in determining the resistance of the wall to this flow. Pieces of porcine thoracic aorta were modified by thermal denaturation, enzymatic digestion or disruptive chemical treatments. The effect of these procedures on the wall content of glycosaminoglycans, collagen and elastin was determined by biochemical assay of uronic acid and hydroxyproline. Effects on hydraulic conductivity were measured by using a flow cell in which tissue was free to deform under applied pressure. Untreated tissue showed considerable variation in uronic acid content but conductivities were substantially less variable and averaged 0.75 x 10(-12) cm4/dyne.s. In tissue autoclaved for < 1 h, resistivity increased, possibly because interstitial components had been denatured but not removed from the wall. After longer periods, resistivity decreased by a factor of one hundred. More specific treatments showed that resistivity decreased by up to a factor of ten when glycosaminoglycans were removed and by a similar factor when collagen was removed. Tissue in which both were removed showed a hundred-fold decrease in resistivity. As with tissue subjected to prolonged autoclaving, the resistivity was still an order of magnitude higher than that of alkali- or acid-extracted elastin despite an apparently similar composition, suggesting the existence of a non-assayed component with important properties. The resistivity of the samples was decreased further by treatment with chymotrypsin, consistent with this component being microfibrillar protein.