The pathophysiology of neuropathic pain in Fabry's disease (FD) is still largely unknown. Seven FD patients were studied by laser evoked potentials (LEPs) to assess the function of the A delta and C fibers. Laser pulses were delivered on the skin of the hand and perioral region at painful intensity to record LEPs related to A delta-fiber inputs and at nonpainful intensity to obtain LEPs related to C-fiber inputs. When the perioral region was stimulated, a vertex positive component was recorded with a mean latency of 260.3 ms and 376 ms after A delta- and C-fiber stimulation, respectively. The mean A delta-LEP amplitude was significantly lower in FD patients (N1/P1 mean values were 2.8 microV and 4.5 microV after hand and face stimulation, respectively, compared to 4 microV and 8.9 microV for controls; N2/P2 mean values were 8.2 microV and 11.1 microV after hand and face stimulation, respectively, and 16.7 microV and 22.3 microV in controls). Unlike the healthy subjects, 6 FD patients, suffering from neuropathic pain, showed a late positive potential related to C-fiber function (mean latency, 377.1 ms) also after facial stimulation at painful intensity, suggesting a relative overflow of C-fiber input, which may be relevant in the pathophysiology of pain in this disease.