For the use of proton exchange membrane (PEM) fuel cell systems to become widespread, the components required to build one should be minimized. Because a PEM fuel cell has a limited operating temperature range, it requires some kind of cooling method. In this study, different cooling methods were investigated experimentally. A PEM fuel cell stack with an active area of 100 cm(2) and 8 cells in series was developed and used in this research. When 50% relative humidity inlet gases were supplied (at 15 A of current discharge and 70 degrees C), cell temperatures at the center increased from around 60 degrees C to 85 degrees C, and cell voltage dropped from 4.8 V to 3.2 V because of membrane drying (insufficient cooling). When fully hydrated inlet gases (100% relative humidity) were supplied to the PEM stack at the same test conditions, the cell temperature remained around 65 degrees C, and stack voltage remained around 5.7 V at 15 A of current discharge. Fully hydrated inlet gases play a positive role both for water transport (when the proton moves from the anode to the cathode) and to maintain the fuel cell stack temperature to prevent stack drying. (C) 2008 Elsevier B.V. All rights reserved.