Swelling, monomer production, polymerization and frictional qualities of test samples of Palocos E, Palacos R and Paladon 65 (Messrs Kulzer & Co, Bad Homburg) have been examined in order to establish which of these plastic substances would be most suitable for replacement of small joints. We found that samples of Palacos E, hardened under pressure of 3.0 kp, had the most favorable qualities.