We describe the expression of mRNA encoding ligands and receptors of members of the GDNF family and members of the neurotrophin family in the adult human spinal cord and dorsal root ganglia (DRG). Fetal human spinal cord and ganglia were investigated for the presence of ligands and receptors of the neurotrophin family. Tissues were collected from human organ donors and after routine elective abortions. Messenger RNA was found encoding RET, GFRα-1, BDNF, trkB, and trkC in the adult human spinal cord and BDNF, NT-3, p75, trkB, and trkC in the fetal human spinal cord. The percentage of adult human DRG cells expressing p75, trkA, trkB, or trkC was 57, 46, 29, and 24%, respectively, and that of DRG cells expressing RET, GFRα-1, GFRα-2, or GFRα-3 was 79, 20, 51, and 32%, respectively. GFRα-2 was expressed selectively in small, GFRα-3 principally in small and GFRα-1 and RET in both large and small adult human DRG neurons. p75 and trkB were expressed by a wide range of DRG neurons while trkA was expressed in most small diameter and trkC primarily in large DRG neurons. Fetal DRG cells were positive for the same probes as adult DRG cells except for NT-3, which was only found in fetal DRG cells. Messenger RNA species only expressed at detectable levels in fetal but not adult spinal cord tissues included GDNF, GFRα-2, NT-3, and p75. Notably, GFRα-2, which is expressed in the adult rat spinal cord, was not found in the adult human spinal cord. J. Comp. Neurol. 440:204–217, 2001. © 2001 Wiley-Liss, Inc.