We have previously described a new and simple method for nerve repair in which continuous longitudinal polyglactin sutures alone are used to bridge limited nerve defects in rats. Here we examined whether such sutures could be used to deliver a growth-promoting substance, triiodothyronine (T3), and enhance regeneration of the rat sciatic nerve. Sutures were pretreated in highly concentrated solutions of T3 for 24 h. In vitro measurements showed that such sutures released T3 with an initial rapid phase followed by a slow-release phase lasting at least 3 weeks. Bilateral sciatic nerve defects (7 mm) in rats were bridged by either T3- or saline-incubated sutures. Immunocytochemistry for Schwann cells and axons at 2 weeks showed no differences in Schwann cell distribution or axonal outgrowth length. Morphometric analysis 4 and 12 weeks after the repair revealed a slight but significant (p < 0.05) increase in the mean myelin area in T3-treated nerves. No differences were seen in the number of axons or return of force in the gastrocnemius muscle at 12 weeks. The results show that sutures can be used both for the bridging of defects in peripheral nerves and for the delivery of a growth-promoting substance to regenerating nerve structures.