We asked whether reinnervating axons are Schwann cell mitogens in vivo as they are in vitro. Left sciatic nerves of 50 Wistar rats were transected. In one-half of the animals, axonal reinnervation from the proximal to the distal stump was allowed to take place, while in the other half, sutures were placed on the transected nerve ends to prevent reinnervation. Samples were collected from 3 days up to 8 weeks after the transection proximally and distally from the point of transection. PCNA-immunostaining was performed on paraffin sections to determine the number of proliferating cells. Axonal reinnervation was followed by Bielschowsky staining and Schwann cell number was determined by counting S-100-immunopositive cells from paraffin sections. In the distal stump Schwann cell proliferation was similar in both experimental groups. There was no statistical evidence of S-100 negative cell proliferation during the study. Proximally to the site of transection the number of small initial axonal sprouts and also the number of Schwann cells increased if the nerve stump had been sutured. In conclusion, although axons may be mitogenic for Schwann cells, axonal reinnervation into the distal stump of the transected peripheral nerve does not influence the proliferation of Schwann cells to a greater extent than other potential effects associated with nerve transection.