Using the indirect immunofluorescence method, the distribution of substance P-like-immunoreactivity was studied in spinal cord and dorsal root ganglia of 25 human foetuses ranging from 12 to 29 weeks of gestational age. The spinal cord and dorsal root ganglia of three infants (1 day-, 2 and 4 month-old) were also investigated as a post-natal reference. On the whole, the substance P distribution patterns seen in infants were already visible throughout most of foetal life. The highest density of substance P-like-immunoreactive fibres was localized over the superficial layers of the dorsal grey horn. Punctiform immunofluorescence was often found over the white matter especially in the funiculi dorsalis et lateralis. In the ventral horn, substance P immunoreactive fibres were few and far between in the grey matter and were only detected from foetal stage 16 weeks. In addition, longitudino-frontal sections through the dorsal regions revealed repetitive arrangements of substance P-like-immunoreactive fibres along the whole spinal cord. In dorsal root ganglia only a few immunoreactive cells were observed. These findings demonstrate the wide and early occurrence of substance P-like-immunoreactivity in the human foetus spinal cord and dorsal root ganglia. They suggest that the development of the substance P neuronal system begins early in ontogenesis and is regionally differentiated.