Oligodendrocytes (OL) isolated from adult pig brains regenerate their processes and form a network of fibers after 14-18 days in vitro (DIV). Stimulation of protein kinase C (Pk-C) by tumour promoters such as 12-O-tetradecanoylphorbol-13-acetate (TPA) produces at day 7 in vitro a similar network after only 20 hr. H-7, an inhibitor of Pk-C, as well as amiloride, which inhibits the subsequent Na+/H+ exchange, reversibly suppress this effect. Activation of the protein kinase A or calmodulin pathway do not result in an increased OL process production. Furthermore, TPA induced proliferation in a subpopulation of OL. We conclude that the stimulation of Pk-C is of utmost importance for OL regeneration.