Surface modification of ultra high molecular weight polyeththylene (UHMWPE) was explored using ion implantation with diffferent dosages (1 X 10(15)-1 X 10(17) ions cm(-2)) of nitrogen. The modified surfaces it.-ere characterised by SEM, nanoindentation and tribological tests. The experimental results showed that ion implantation can significantly increase the surface hardness of UHMWPE. However, the improvement in it-ear resistance of the modified UHMWPE is highly dose dependent. Compared with the untreated material, the low dose implanted UHMWPE exhibited a three fold improvement in wear resistance, while the high close ion implanted material showed hardly any improvement although it possessed the highest hardness. (C) 2003 IoM Communications Ltd. Publishcd by Maney for the Institute of Materials, Minerals and Mining.