Messenger RNA, obtained from post-mortem brain of 10 schizophrenics, five depressed patients and 10 control subjects, was characterised with respect to a number of parameters. It was found that post-mortem delay was not the major factor in determining RNA yield, size (as determined by cDNA synthesis) and biological activity. Biological activity, as determined by in vitro translation in a reticulocyte-lysate system, could be observed using messenger RNA from periods of 0 to 84 hours post-mortem. Two-dimensional gel analysis of the newly-synthesised radiolabelled products obtained from this material revealed several hundred individual species but no consistent degradation of any particular species with post-mortem delay. It is suggested, therefore, that premortem changes are as important as post-mortem changes in determining RNA yield, size and biological activity. Although no consistent difference could be found between patients and controls using any of these parameters, this study confirms that, by isolating messenger RNA from post-mortem human brain, valuable information can be gained on gene expression in psychiatric disorders.