Ultra high molecular weight polyethylene (UHMWPE) wear particles are frequently implicated in causing failure of total joint arthroplasties by eliciting a foreign body reaction. The majority of these particles are subcellular and many are submicron in size. Identification of these small particles of UHMWPE by conventional histologic techniques is difficult. We have therefore investigated the utility of Oil Red O (ORO) stain to identify UHMWPE on histologic sections. A wide variety of specimens was studied including an experimental rabbit model with subcutaneous implantation of polyethylene particles as well as specimens from clinical cases with joint arthroplasties. The sensitivity and specificity of ORO stain was compared to conventional polarized light microscopy for the identification of particulate UHMWPE debris. The ORO stain was found to be as sensitive in identifying particulate UHMWPE debris as polarized light microscopy. However, ORO stain was less specific: two specimens did not contain any UHMWPE also stained with ORO. Careful examination of standard hematoxylin and eosin stained sections with polarized light was therefore more specific for the identification of particulate UHMWPE. As a single test, the ORO stain does not appear to offer any clear advantage specifically for the identification of UHMWPE.