Tyrosine hydroxylase (TH)- and peptide-immunoreactivity of postganglionic neurons and of nerve fibres in guinea pig lumbar paravertebral sympathetic ganglia 2–4 after transection of the communicating rami and the visceral branches, respectively, were investigated by single-and double-labelling techniques. Six subpopulations of postganglionic neurons were discriminated immunohistochemically: two cell types, which were immunoreactive to only one of the applied antisera — TH, and vasoactive intestinal polypeptide (VIP); and four cell types in which immunoreactivity was colocalized — TH/neuropeptide Y (NPY), NPY/VIP, dynorphin/α-neoendorphin and dynorphin (α-neoendorphin)/NPY. Small intensely fluorescent (SIF) cells dependent on their location exhibited differential immunobehaviour to NPY-/dynorphin-(α-neoendorphin-) and TH-antisera. Immunoreactivity to substance P (SP), calcitonin gene-related peptide (CGRP), met-enkephalin-arg-phe (MEAP) and leu-enkephalin was present in nerve fibres but not in postganglionic neurons with frequent colocalization of SP/CGRP- and MEAP/leu-enkephalin- and, sometimes leu-enkephalin/SP- and dynorphin/SP-immunoreactivity. TH-immunoreactive intraganglionic nerve fibres were numerically more increased after cutting the visceral branches, than after transection of the communicating rami. Vice versa, NPY-, VIP-, dynorphin- and α-neoendorphin-immunoreactive nerve fibres were particularly increased in number after cutting the communicating rami. Many but not all of the nerve fibres exhibited colocalization of two of these peptides. SP-, CGRP-, and enkephalin-immunoreactive nerve fibres were not visibly affected by cutting the visceral branches but virtually disappeared after lesioning the communicating rami.