In this study, we investigate the innervation to the feline ophthalmic artery by the horseradish peroxidase (HRP) tracing method. Five adult cats with body weights ranging between 2.0 and 3.0 kg were used. Under microscopic dissection, the ophthalmic artery was identified and isolated. A gelfoam (Upjohn Co.), 1 x 3 mm in size, containing 0.1 ml of HRP was applied to the prepared artery segment for 2 h. The cat was sacrificed 3 days later. The trigeminal, stellate, superior cervical, middle cervical and nodal ganglia, and oculomotor, trochlear and abducens nuclei were removed, sectioned and stained for HRP-positive cells. HRP-labeled neurons were found in the ipsilateral trigeminal (TRG) and superior cervical ganglia (SCG). The middle cervical, stellate, Edinger-Westphal, trochlear and abducens nuclei were all deemed negative for HRP-labeled cells. In the TRG, HRP-labeled neurons ranged from 21 to 250 (mean +/- SE = 93.8 +/- 42.5/ganglion). The labeled neurons were distributed primarily in the ophthalmic branch. In the SCG, the HRP-labeled neurons were distributed evenly in the ganglion, ranging from 6 to 180 (mean +/- SE = 91.6 +/- 31.5/ganglion). Two additional cats having received a sham operation revealed a negative finding. The feline ophthalmic artery is innervated by the ipsilateral TRG and SCG. Such innervation may play a role in regulating blood flow to the optic nerve.