Non-steroidal anti-inflammatory drug (NSAID)-induced increased small-intestinal permeability appears to be a prerequisite for the development of NSAID enteropathy, which is a cause of much morbidity in patients with rheumatoid arthritis. We assessed, with a combined absorption-permeability test, the effects of Carbopol® (a polyacrylic acid polymer capable of increasing mucus strength and viscosity) on intestinal function and whether it protected against indomethacin-induced increased intestinal permeability. Using a test solution of 3-0-methyl-D-glucose, D-xylose, L-rhamnose, and ⁵¹Cr-labelled ethylenediaminetetraacetic acid with 5-h urine collections for marker analyses, we tested 16 subjects, as base line, after 20 ml Carbopol 4 times daily for 4 days, after indomethacin alone (75 + 75 mg), and after coadministration of Carbopol and indomethacin. Carbopol had no significant effect on the permeation or absorption of the test substances. Indomethacin increased intestinal permeability significantly, and this was unaffected when Carbopol was coadministered with indomethacin, showing that Carbopol does not limit the immediate damage of NSAIDs on the small intestine.