Several high-affinity analogs of neuropeptide FF (Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH 2 , NPFF) exhibiting both supraspinal anti-opioid and spinal analgesic activities were studied for their abilities to interact with specific μ, δ, and κ opioid binding in the rat spinal cord. Measurements by quantitative receptor autoradiography in the superficial layers of the spinal cord revealed that NPFF analogs tested have only a low affinity for opioid receptors since K i values ranged from 5 to 400 μM. Taking into account the high efficacy of NPFF after intrathecal injection, these results indicate that analgesic effects of NPFF did not result from opioid receptor stimulation.