High-resolution multiple two-dimensional polyacrylamide gel electrophoresis (ISODALT) has been used to analyse soluble protein extracts from human brain and 12 other human organs. Approximately 200 protein gene products can be visualised on an electrophoretogram of soluble human brain proteins. By electrophoresing extracts of different human organs separately and mixed with brain extract, 8 proteins have been found which appear to be present in brain in concentrations at least 20 times greater than in any other organ. Four of these brain-specific proteins have been identified by co-electrophoresis with purified proteins as 14-3-2 protein, creatine kinase-BB isoenzyme, aldolase C4 isoenzyme, and 14-3-3 protein. The identities of the remaining 4 proteins are unknown.