Twenty-six hands in 26 adults with osteoarthrosis of the thumb trapeziometacarpal joint were randomised to undergo either trapeziectomy alone (control) or with the interposition of porcine dermal collagen xenograft (Permacol). The study was terminated prematurely because of apparent reactions to the implants in six of 13 patients. The collagen interposition group required more frequent review on clinical grounds and were discharged later after surgery. Three of the implants have been removed and histology revealed foreign body reactions in all. There was no difference in thumb movement or power after surgery between the two groups. However, improved grip strength was observed and improved function were reported only in the control group. Permacol patients reported greater pain and were less satisfied with their operations than control patients. We conclude that interposition of Permacol is detrimental to the results of trapeziectomy.