Eleven surgically retrieved stainless steel implants showing varying degrees of surface corrosion were examined to characterize the morphology and composition of corrosion products. The implants were fabricated to the specification AISI316L (Muller) and BS 3531 pt 1 1971-78 (Charnley). They had been in place for 9-21 y (Mean :13 y) and failures were due to aseptic loosening. The morphology and chemical compositions of corrosion products were recorded using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Nine implants had areas of corrosion covering 1-5 cm of the stem, partially or all round. Corrosion existed in layers. The layers consisted either of chromium in association with sulfur, or iron in association with phosphorus. Variable amounts of calcium and chlorine were also present in all layers. Nickel, which makes up 13% of the alloy, was persistently absent. The presence and extent of corrosion was independent of the alloy composition and could not be related to the duration of implantation.