Selective activation of A or C nociceptors may enable focused study of changes occurring in various pain states. Infrared diode laser irradiation uniformly heats skin and was used for 2 types of stimuli: short duration (50-200ms, 3 mm2)-high intensity (high heating rate) pulses, which produce a pricking pain sensation in humans and reflex withdrawal in rats, or long-duration (1.5-20s, 40 mm2)-low-intensity (low heating rate) pulses, which produce a burning pain sensation in human and withdrawal in rats. We performed in vivo, intact-brain, extracellular single-unit trigeminal ganglion neuron recordings during laser stimulation of the face in adult male SD, isoflurane-anesthetized rats. Trigeminal ganglion neurons which responded to low rate (15s) laser stimulation of the face in a graded, intensity-dependent manner had a nerve conduction velocity (NCV) of approximately 1.0 m/s (C-fibers). Some of these units were sensitized by topical capsaicin application, but did not respond to short-pulse (up to 200 ms) laser stimulation of any intensity, providing evidence for selective nociceptor activation. Nociceptive units responding to high rate laser stimulation and conducting at velocities corresponding to A-fibers (1.5 > NCV < 5 m/s) were also recorded, and generally did not respond to the low heating rate laser pulse. These units were sensitized by topical Dimethylsulfoxide (DMSO). In addition, we measured skin temperature during some experiments using a thermocamera (FLIR) with fast time resolution. These data are consistent with human psychophysics and previously published behavioral pharmacologic results, and provide evidence that low heating rate laser stimulation selectively activates C thermonociceptors and that high rate stimuli activates only A nociceptors. This paradigm may provide an electrophysiological model for selectively investigating the response properties of nociceptive neurons in normal and pathological states.