A new and serious complication was experienced by patients of three independent surgeons following routine augmentation procedures. In each case reported, double-lumen prostheses had been used. All cases were reoperated with a diagnosis of capsular contracture. However, at surgery it was found that the outer lumen of the prostheses had overfilled with 60-160 cc of interstitial fluid, probably because of an osmotic gradient. The possible causes of this unfortunate complication are considered.