In the present study, the authors reevaluated the temporal course and properties of neurotrophic activities present in the fluid accumulating in the silicone-chamber model for nerve regeneration. The fluid collected from silicone chambers was tested in four different dissociated neuronal cell cultures. Furthermore, the activity of the chamber fluid was examined, using a cell blot technique. There was one major peak of neurotrophic activity and this activity peaked early, about 3 to 6 hr after nerve injury. Results also indicate that the chamber fluid contains at least two types of neurotrophic activities, namely nerve growth factor and ciliary neurotrophic factor.