1. We have examined the effect of intravenously injected nitro-L-arginine methyl ester (L-NAME), inhibitor of nitric oxide (NO) synthase, on the ongoing discharges originating in dorsal root ganglia in rats. 2. Ongoing activity was recorded from dorsal rootlets that were responsive to electrical stimulation of the axotomized sciatic nerve. Resection of the nerve proximal to the neuroma did not appreciably influence the rate of ongoing activity. Intravenous L-NAME (100 and 200 mumol/kg) suppressed ongoing activity both when the neuroma was intact or acutely resected. The effect of L-NAME was reversed by L-arginine (575 and 1,150 mumol/kg). 3. L-NAME had no effect on ongoing activity recorded from dorsal rootlets in normal rats or rootlets with no sciatic input in axotomized rats. 4. No ongoing activity could be recorded from sciatic nerve filaments that had been sectioned proximally before the recording in axotomized rats, although a response could be elicited by mechanical stimulation of the neuroma. 5. Because peripheral axotomy has been shown to markedly increase the level of mRNA for NO synthase in dorsal root ganglion cells, the present results indicate that NO may be involved in the generation of spontaneous discharges in deafferentated dorsal root ganglia.