The stability of somatostatin (SS) in brain tissue was studied in human material obtained post-mortem and in the rat. In both human and rat brain, loss of SS was found to occur in tissue frozen to -70 degrees C. In the rat, this loss varied from 26 to 70 percent depending on the type of tissue processing used. These data suggest that, for the study of SS in post-mortem brain, use of frozen material should be avoided.