Transforming growth factor-beta 1 (TGF-beta 1) is highly expressed in neural tissues following brain injuries. To determine a role of TGF-beta 1 in neural pathologies, axons of cultured rat hippocampal neurons were cut by local irradiation of laser beam, and the effect of TGF-beta 1 on neurite regeneration following axotomy was investigated. The axonal growth was stopped by laser irradiation, but addition of TGF-beta 1 remarkably promoted the axonal re-elongation from the injured site. The effect of TGF-beta 1 was concentration dependent and seen maximally at a concentration of 1 ng/ml. These results suggest that TGF-beta 1 has a capability of promoting axonal regeneration of brain neurons after lesioning.