The human gallbladder was investigated by means of immunohistochemical methods for the occurrence of peptidergic nerve fibres. In the gallbladder 11 types of peptidergic nerve fibres were observed. These were somatostatin-, pancreatic polypeptide (PP)-, peptide YY (PYY)-, neuropeptide Y (NPY)-, vasoactive intestinal peptide (VIP)-, gastric inhibitory peptide (GIP)-, neurotensin-, cholecystokinin (CCK)/gastrin C-terminus, substance P-, galanin- and serotonin-immunoreactive nerve fibres. NPY- and GIP-containing neurones were occasionally observed in the ganglionated plexus in the fibromuscular coat. Somatostatin-, NPY-, neurotensin-, and galanin-immunoreactive nerve fibres were abundant. The other nerve fibres were few. Peptidergic nerve fibres occurred in the lamina propria mucosae around and in close contact with the basement membrane of the epithelial cells. In the fibromuscular coat, they lied mainly around the muscle bundles. They showed no special arrangement in the perimuscular connective tissue. In both arteries and veins somatostatin-, neurotensin, and galanin nerve fibres were detected in both tunica media and tunica adventitia. NPY-nerve fibres were found in tunica media and substance P- and GIP- nerve fibres in tunica adventitia. The peptidergic nerve fibres observed in the gallbladder outnumbered those observed with the peripheral nerve markers used in this study. It has been speculated that this might be due to the coexistence of several neuropeptides in the same nerve fibre and/or the coexistence of these neuropeptides with a classical neurotransmitter.