In an effort to fabricate cost effective and reliable carbon monoxide sensors, the humidity dependence of the carbon monoxide oxidation rate has been studied. Using a simple electrochemical cell based on the hydrogen form of Nafion(R) 117 as the electrolyte, the carbon monoxide oxidation rate has been determined to be a linear function of the ambient humidity at room temperature. The oxidation current, or the sensor response has been observed to increase linearly with increasing humidity. The sensor response to carbon monoxide was also found to increase Linearly with increasing carbon monoxide concentrations for concentrations less than 200 ppm. The signal to noise ratio was determined to increase from 15.8 to 47.8 with increase in humidity from 12 to 64%.