Summary Seventeen patients with long-lasting idiopathic trigeminal neuralgia (ITN) were treated with either five, weekly peripheral streptomycin/lidocaine (S/L) or lidocaine alone injections, in a double blind controlled study. Eight patients responded initially to the treatment in the S/L group and three patients in the lidocaine group. Pain recurred in four patients from the S/L group within two weeks and six months following the last injection. One patient from the lidocaine group remained pain-free for eight months. At the final assessment, three patients from the S/L group and two patients from the lidocaine group remained pain-free up to 30 months. Neither treatment affected sensory functions of the injected nerves. It is concluded that S/L injections are initially effective in the treatment of ITN. In the long term, however, their effects are similar to the effects of lidocaine alone.