The immunohistochemical occurrence of trkA, trkB and trkC receptors was examined in the human trigeminal ganglion and spinal nucleus of subjects at all ages and compared with that of substance P (SP) and calcitonin gene-related peptide (CGRP), trk-like immunoreactive (LI) material was detectable in discrete subpopulations of primary sensory neurones from 25 weeks of gestation to adult life. Each subpopulation overlapped partially with those immunoreactive to SP and CGRP, trkA- and trkC-positive filamentous and punctate elements occurred in the trigeminal subnucleus caudalis. While immunostaining for trkC was restricted to rare isolated elements, that for trkA outlined the superficial laminae of the nucleus and was more intense early in life than in adults.