Preliminary results have been obtained on the biocompatibility of amorphous carbon hydrogen (αC:H) coatings deposited on polystyrene. Deposition was carried out at low substrate temperatures using pulsed r.f. plasma-assisted chemical vapour deposition from a methane-hydrogen gas mixture. Cytotoxicity tests using a standard cell line indicate a high degree of biocompatibility. Specifically, αC:H is not toxic to cells, appears to increase cell attachment and affords normal cell growth rates. Wear and other tests have revealed no significant differences between these αC:H coatings and those deposited on a stainless steel at a higher substrate temperature, except for a more pronounced surface texture. However, position in the r.f. plasma was found to be critical for the deposition of good, adherent low temperature coatings.