To investigate the neuronal migration and synthesis of peptidic neurotransmitters in vitro, neuromuscular co-cultures of nodose ganglia and cardiac muscle cells of Wistar rats were established. The living cells of co-cultures were observed with an inverted contrast microscope at different culture age. At 72 h and 96 h of culture age, the neuromuscular co-cultures were examined by Holmes' reduced silver staining technique for observing the neuronal migration. Immunohistochemical staining method was used for investigating the synthesis of peptidic neurotransmitters- substance P (SP) and calcitonin gene-related peptide (CGRP). The neuronal morphorlogical maturation in neuromuscular co-cultures seems at 72 h of culture age in terms of the observation of living cells and Holmes' reduced silver staining technique. SP- and CGRP-immunoreactive neurons were observed in neuromuscular co-cultures at 96 h of culture age but not 72 h. The results indicate that the neuronal morphological maturation can not represent the maturation of neurotransmitter synthesis. The synthesis of neurotransmitters is not maturated in the neuromuscular co-cultures until 96 h of the culture age.