Cerebrospinal fluid (CSF) and serum samples from 361 consecutive patients were investigated. The protein pattern of each sample was examined by isoelectric focusing (IEF) of unconcentrated CSF followed by silver staining and by agar gel electrophoresis of concentrated CSF stained with amido black. 347 paired samples were compared. The results were the same in 83% of the samples. Discordant results were found in 10% of the samples. and in 7% additional information was achieved by one of the methods. IEF was superior to agar gel electrophoresis for the identification of oligoclonal immune reactions of the central nervous system. Tau globulin increase was seen in a few CSF samples, more often with IEF and then associated with other changes of the pattern. IEF of unconcentrated CSF followed by silver staining only requires 20 microliters CSF, while 3-4 ml CSF is needed for the agar gel electrophoretic method. It was concluded that IEF has several advantages compared to agar gel electrophoresis and is suitable as a routine method in clinical laboratories.