Single wall carbon nanohorns (SWNH), produced by AC arc discharge in air, were used as Pt and PtRu supports in polymer electrolyte membrane fuel cells (PEMFC). These electrocatalysts were compared with equivalent electrocatalysts supported on commercial carbon back. The SWNH were characterized by differential thermal analysis (DTA), TEM, SEM, and XRD. The produced SWNH were 84.5 wt% pure, containing 3 wt% of amorphous carbon and 12.5 wt% of graphitic carbon. SWNH were used as electrocatalyst supports and tested in the electrodes of two types of polymer electrolyte fuel cells: H(2)-fed PEMFC and direct methanol fuel cells (DMFC). The electrocatalyst nanoparticles anchored on both carbon supports were ca. 2.5 nm in diameter obtained by employing ethylene glycol as the reducing agent. The use of SWNH showed catalytic activities 60% higher than using carbon black as the electrocatalyst support in both types of fuel cells.