Levels of nerve growth factor (NGF) in rat hindpaw skin, measured with a sensitive two-site enzyme-linked immunosorbent assay, show two peaks during normal development. The first (57 ± 5 pg mg−1) occurs at embryonic days (E) 18–20 and coincides with the arrival of axon terminals into the hindpaw skin. The second, larger peak (132 ± 10 pg mg−1), occurs later, around postnatal day (P) 21 and may be involved in maintenance of neuronal phenotype. Levels outside the two peaks stay relatively constant throughout development (30 pg mg−1). Skin wounding at birth produces a marked increase in NGF levels (149 ± 25 pg mg−1) which declines after 4 days. This large increase is not observed if wounding is performed at older ages and may underlie the sensory hyperinnervation that accompanies neonatal wounds.