Abstract Antisera were prepared against the PC12 clonal line of rat pheochromocytoma both before and after treatment of the cells with nerve growth factor. PC12 cells untreated with nerve growth factor (PC12-) bear phenotypic resemblance to adrenal chromaffin cells while nerve growth factor-treated PC12 cells (PC12+) extend neuntes and acquire many properties of sympathetic neurons. A cell culture complement-mediated cytotoxicity assay was used to detect differences between the abilities of antisera to PC12- and of antisera to PC12+ to recognize surface antigens on cell bodies and on neurites of PC12 cells and rat sympathetic neurons. For example: (1) Antisera to PC12- possessed much more potent cytotoxic activity against PC12- cells than did antisera to PC12+. (2) While antisera to PC12-possessed potent cytotoxic activity against both cell bodies and neurites of PC12+ cells, antisera to PC12+ showed higher titers against neurites than against cell bodies. (3) Antisera to PC12+ possessed potent cytotoxic activity against rat sympathetic neurons while antisera to PC12- showed no cytotoxic activity against such cells. At appropriate dilutions, antisera to PC12+ caused preferential destruction of neurites in cultures of PC12+ cells and sympathetic neurons. The cell bodies which were left intact after such treatment were capable of rapid neurite regeneration following removal of the antiserum. Such differences in cytotoxic activities of the antisera appear to reflect differences in the antigenic composition of the cells against which they were prepared; cross absorption experiments indicated that such differences were, however, quantitative rather than qualitative. Absorption with brain and adrenal tissue suggested that the antisera recognize classes of cell surface antigens which are 1. (1) shared by adrenal and neural tissue, 2. (2) specific to adrenals, 3. (3) specific to neural tissue, and 4. (4) present on PC12 cells but not in either brain or adrenal tissue. The properties of the antisera suggest that they will be useful for identification, characterization and localization of neural and adrenal medullary surface antigens.