During total hip replacement, the reamed medullary canal of the femur should represent a clean, dry surface. We compared the effectiveness of 4 different cotton swabs in a synthetic femur that had been reamed to receive a size 1 Exeter trial prosthesis. Swab sizes included a 2.5 cm and a 7.5 cm diameter ribbon gauze, a pair of 10 x 7.5 cms square swabs and a larger surgical packing swab (20 x 22 cms). The ability of the swabs to pack the femur was assessed using both plain radiographs and colour photography (after femoral section). After retrieval from the canal, the total dry weight of the cotton inserted was recorded as was the time required to withdraw each swab type. Only the narrowest (2.5 cm diameter) ribbon gauze was found to achieve comprehensive packing as far as the cement restrictor but it required a longer time for removal, and there may be a case for using larger ribbon gauze in larger femora. The mass of cotton delivered to the canal using small square swabs was half of that delivered using narrow ribbon gauze.