Data are reported for Gore's advanced PRIMEA(R) membrane electrode assembly (MEA) series 5561 exposed to relatively high concentrations (500, 3,000 and 10,000 ppm) of CO in hydrogen at 202 kPa and at 70 and 90degreesC. The steady-state and transient measurements obtained in this study at low reactant stoichiometry and 202 kPa are compared with earlier results 1 for atmospheric conditions to show the effect of temperature and pressure on the poisoning and recovery rates. All data are reported for a 25 cm(2) laboratory-scale proton exchange membrane fuel cell (PEMFC) using CARBELT(TM) GDM CL gas diffusion media (GDM) for conditions with and without air-bleed treatments. For 500 ppm CO/H-2 mixtures without air-bleed, the performance at 202 kPa and 0.6 V provides a steady-state current density of 1.0 A/cm(2) at 90degreesC but only 0.4 A/cm(2) at 70degreesC. At 101 kPa and 70degreesC, exposure to 500 ppm CO/H-2 mixtures requires 5% air-bleed to obtain this performance. Transient experiments with these CO levels indicate that there is up to a four time decrease in the poisoning rates at 202 kPa vs. 101 kPa. Further at 202 kPa, increasing the cell temperature from 70 to 90degreesC results in approximately a fourteen time decrease in the poisoning rate for 3,000 ppm CO/H-2 mixtures and approximately four time decrease for 10,000 ppm CO/H-2 mixtures. The data discussed in this paper are suitable for verifying numerical models of a PEMFC and establishing a baseline for new recovery schemes using new MEAs with enhanced CO tolerance. In addition, the results have implications for the design of reformate fuel-processing systems and the use of effective control schemes to prevent CO transients.