The effect of a single dose of capsaicin administered neonatally on the development of six motor behavioral patterns (scratching, rearing, grooming, searching, remaining still, and sniffing) was examined in Wistar rats. Treated animals exhibited a significant increment in scratching, rearing, grooming, and searching. Capsaicin also provoked precocious eye opening of one to two days and a reduction in remaining still, sniffing, and body weight. These effects were accompanied by pelage dishevelment and presence of skin ulcers in the region of the head, neck, and shoulders. The distribution of skin ulcers suggests that the fifth cranial nerve and roots innervating C1-C3 spinal cord segments contain a high proportion of capsaicin-sensitive "C" and A delta fibers.