The deep lying, large output neurons of the olfactory tubercle have been implicated as being pallidal-like; therefore it seems likely that this region of tubercle could be a rostro-ventral extension of the globus pallidus. Evidence exists that pallidal neurons concentrate iron in the form of proteinaceous ferritin, and therefore may be uniquely identified using immunocytochemical methods. Since normal histochemical techniques designed to demonstrate iron have failed, probably because of the state of the iron within the ferritin molecule, the immunocytochemical method is being pursued to detect the ferritin. This method requires: (1) the extraction of ferritin from rat tissue; (2) injection of ferritin as antigen into rabbits; (3) extraction of antibodies from rabbit serum; (4) column chromatography of antibody sera to increase the specificity of the antibody-antigen reaction; and (5) application of sera to forebrain sections for demonstration of ferritin-containing cells. Other histochemical studies showed that: a) The acetylcholinesterase (AChE) stain of a skate brain to be of low intensity in striatum but heavy in brainstem areas; b) Although striatal AChE in oppossum appeared typical, distinct patterns were present in frontal cortex and the trigeminal nucleus.