The sensory axons of the adult frog sciatic nerve with the attached dorsal root ganglia have previously been found to regenerate in vitro providing the nerve was subjected to a lesion in vivo 10-17 days earlier. We show here that the lesion in vivo is not a prerequisite for regeneration in vitro. If the freshly dissected nerve is subjected to a local crush there is an initial delay of 3.4 days after which the sensory axons start to elongate in vitro at a rate of 1.1 mm.day-1. Transformation of the cultured nerve into a growth state is reflected by similar changes in the electrophoretic distribution of rapidly transported proteins in the sensory axons as could be shown to take place during regeneration in vivo. The onset of the regeneration process is partially arrested by inhibition of proliferation of satellite cells by ara-C, in contrast to subsequent mechanisms required to maintain the outgrowth of new axons. The present system opens new possibilities to study in vitro the early events of the regeneration program as well as later steps concerned with the elongation of new axons within an adult vertebrate peripheral nerve.