Brain-derived neurotrophic factor (BDNF) is a survival factor for certain sensory neurons during development. Using electrophysiology in BDNF-deficient mice, we show here that slowly adapting mechanoreceptors (SAM), but not other types of cutaneous afferents, require BDNF in postnatal life for normal mechanotransduction. Neurons lacking BDNF did not die, but instead showed a profound and specific reduction in their mechanical sensitivity, which was quantitatively the same in BDNF -/- and BDNF +/- animals. Postnatal treatment of BDNF +/- mice with recombinant BDNF completely rescued the mechanosensitivity deficit. Therefore BDNF is important for regulating SAM mechanosensitivity, independent of any survival-promoting function.