In both vertical banded gastroplasty and in gastric banding, synthetic bands are used to reinforce the outlet from the pouch to the rest of the stomach. Two materials commonly used for these bands are polypropylene (Marlex) and polytetrafluoroethylene (GORE-TEX). As a measure of their suitability, human inflammatory response to subcutaneous implants was investigated. In a randomized series of 17 superobese patients a patch of GORE-TEX was implanted subcutaneously in one groin under local anaesthesia and Marlex mesh was implanted in the other groin. After about 2 months the implants were exstirpated and investigated in a single blind procedure by an experienced pathologist. Marlex gave a significantly greater chronic inflammatory reaction and fibrosis than GORE-TEX. The foreign body giant cell reaction was, however, significantly greater with GORE-TEX. The possible implications of these results are discussed.