The clonal rat pheochromocytoma, PC12, responds to nerve growth factor (NGF) and dibutyryl adenosine cyclic 3′:5′monophosphate (dbc AMP) by the elevation of cellular protein and RNA levels in all three parameters that are additive or greater than the sum of those caused by either agent alone, indicating that the mechanisms by which the two agents act to produce these changes are distinct. The concentration of dbcAMP required for half-maximal stimulation of these changes is also different for each, while NGF is active in all instances at 10(-11) M. PC12 cells initially generate neurites slowly in response to NGF and, at the same time, develop the capacity to regenerate neurites rapidly, a process termed priming. The cells, however, are not primed by dbcAMP nor does it influence the ability of NGF to prime them. Time lapse cinematography demonstrates that both NGF and dbcAMP each have unique effects on cellular morphology. The latter produces' rapid, unstable neurite initiation but does not promote sustained neurite extension. In contrast, NGF has immediate effects at the cell surface with no neurite initiation but later produces sustained neurite outgrowth. Utilizing dbcAMP, it is possible to dissect four morphological response of PC12 cells to NGF. Three of these may be mechanistically closely tied to occupancy of the NGF plasma membrane receptor.