Measurements have been made of dopamine, noradrenaline, glutamate decarboxylase (GAD) and choline acetylase (CAT) in a variety of regions from human post-mortem brain tissue, and the results analysed as a function of ante-mortem and post-mortem factors which may influence such measurements. The agonal status of the patient emerged as a major influence on the post-mortem measurement of GAD activity, without significantly affecting the other biochemical parameters. Of the other ante-mortem factors investigated, there appeared to be no differences between male and female, no circadian fluctuations, and few significant age-related changes, in any of the biochemical parameters measured in different brain regions. Moreover, the results indicated that the enzymes GAD and CAT are remarkably stable in human brain during routine post-mortem handling. Similar findings were made for dopamine and noradrenaline, although a substantial loss of both catecholamines probably occurs in the first few hours after death.