Trigeminal mechanoreceptive afferent fibers associated with either mystacial vibrissae or rhinarial receptive fields were isolated for single unit analysis by either microdissection of infraorbital nerve fibers or microelectrode recording from the trigeminal ganglion.Receptive fields of all but two of the 238 vibrissa units were confined to single vibrissae. 47% were rapidly adapting (RA), and 53% were slowly adapting (SA). 10% of the SA units displayed a resting discharge in the absence of mechanical stimulation. Different vibrissa units were found to respond to movements in from one to six primary directions (anterior, dorsal, posterior, or ventral deflection, pushing, pulling); the modal unit responded to deflection in two adjacent primary directions, plus pushing. No systematic relationships were found between directional sensitivities and either length of vibrissa or location of the vibrissa on the mystacial pad. However, SA units were somewhat more directionally sensitive, and were more likely to respond to pushing than were RA units. Each vibrissa is innervated by many units, differing in their response properties.The 25 rhinarial mechanoreceptors displayed unitary, punctiform receptive fields. Eight were RA; 17 were SA. No rhinarial unit of either type displayed a resting discharge. The relationship between velocity of skin indentation and unit discharge rate during indentation of rhinarial receptive fields was best described by a power function for both RA and SA units.