 This is a double-blind, randomised, parallel-group comparison of ethyl-EPA and placebo in the treatment of established TD in patients with schizophrenia or schizo-affective disorder. There will be a pre-trial screen, following which subjects will enter the randomised treatment phase for 12 weeks. Responders will then be offered the option of open add-on treatment with ethyl-EPA for a further 40 weeks. 