From the results of previous studies in which developing peripheral ganglia from quail embryos were transplanted into younger chicken embryo hosts, we concluded that spinal and cranial sensory ganglia contain dormant precursors with autonomic potentialities. Here we describe the differentiation of these precursors in vitro, from dorsal root and nodose ganglion cell suspensions. Dorsal root ganglia were removed from quail embryos at 9 to 15 days of incubation, dissociated to single cells, and grown in tissue culture. The differentiation of cells with autonomic features was followed by monitoring properties associated with the adrenergic phenotype (absent from quail sensory ganglia during normal embryonic development). Provided that the medium was supplemented with chicken embryo extract, numerous cells displaying tyrosine hydroxylase immunoreactivity could be detected from day 4 onward. They possessed long, multiple processes but appeared morphologically distinct from primary sensory neurons. The catalytic activity of tyrosine hydroxylase and of other enzymes required for catecholamine production was demonstrated in the cultures by glyoxylic acid-induced histofluorescence and by radiochemical measurement of the conversion of exogenous tyrosine to norepinephrine. A large proportion of tyrosine hydroxylase-positive cells were found to incorporate [3H]thymidine before and after differentiating. In contrast, recognizable sensory neurons never exhibited adrenergic properties and did not divide. Qualitatively similar results were obtained with cultures of dissociated nodose ganglia. These findings lend further weight to the assumption that latent autonomic precursors are included in the non-neuronal compartment of sensory ganglia.