1. The influence of sympathetic and parasympathetic nerve stimulations on salivary secretion of immunoglobulin A (IgA) was studied in the submandibular glands of anaesthetized rats by stimulating the nerve supplies with bipolar electrodes. 2. Although the flow of saliva from sympathetically stimulated glands was only 23% of that from parasympathetically stimulated glands the output of IgA was over 2-fold greater. This difference was attributable to influences of the nerves on IgA secretion through the epithelial cell polymeric immunoglobulin receptor-mediated pathway, as Western blotting with specific antibodies to IgA and secretory component revealed that secretory IgA (SIgA) dominated in all saliva samples. 3. Study of saliva secreted in sequential periods of nerve stimulation or following rest pauses suggested that SIgA secretion occurred in the absence of stimulation but this was upregulated 2.6- and 6-fold by parasympathetic and sympathetic nerve stimulations, respectively, compared with the calculated unstimulated rate. 4. The IgA content of extensively stimulated glands was 77% of levels in unstimulated contralateral control glands despite a secretion into saliva equivalent to almost 90% of the glandular IgA content. The IgA may be synthesized and secreted by glandular plasma cells at a rate which exceeds demand and/or such synthesis may be upregulated by nerve impulses. 5. The results indicate that salivary secretion of SIgA is upregulated by nerve impulses and that sympathetic nerves induce a greater effect than parasympathetic nerves.