In the goldfish brain, eleven groups of tyrosine hydroxylase (TH) -positive (catecholaminergic neurons and four groups of serotonin (5-HT) -positive (serotonergic) neurons are described as follows by immunofluorescence and light microscopic level of PAP technique: 1) The olfactory bulb (TH); 2) The area ventralis telencephali (TH); 3) The nucleus preopticus (TH); 4) The nucleus dorsolateralis thalami (TH); a) The pretectal area (5-HT); 5) The nucleus ventromedialis thalami (TH); 6) The nucleus posterioris periventricularis (PVO-accompanying cells) (TH); b) The nucleus recessus lateralis (NRL) (5-HT); 7) The rostro-medial part of the nucleus recessus lateralis (NRL) or the paraventricular organ (PVO) pars anterior (TH); b) PVO pars anterior (5-HT); 8) The nucleus posterior tuberis (NPT) (TH); c) The nucleus recessus posterioris (NRP) (5-HT); 9) The lateral isthmal region (TH); d) The raphe nuclei of the brainstem (5-HT); 10) The reticular formation of the medulla oblongata (TH); and 11) The post-obecular region (TH).By immunoelectron microscopy, two kinds of cerebrospinal fluid (CSF) -contacting neurons were confirmed in the PVO pars anterior. One contained TH-positive granules (80-120 nm) and the other 5-HT-immunoreactive granules (100-200 nm in diameter). In the telencephalon, preoptic nucleus (PON) and nucleus posterior tuberis (NPT), TH-positive non-CSF-contacting neurons showed similar ultrastructure such as well developed rough surfaced endoplasmic reticulum, and immunoreactive granules (106-110 nm).