The contamination effect of formaldehyde (HCHO) and formic acid (HCOOH) was studied using state-of-the-art automotive PEMFC stacks and with high fuel utilization and automotive-type operation with hydrogen recirculation. The results, measured at current density of 0.6 A/cm(2), show that the contamination effect of formaldehyde was observable when the concentration was 2 ppm, 200 times higher than the current limit in the ISO 14687-2:2012 standard. The effect of formaldehyde was less than 10% compared to 2 ppm of CO in the same operating conditions. Moreover, the contamination effect of formic acid was barely measurable at 2 ppm, corresponding to a concentration 100 times the limit of the ISO standard. Thus, the limits of HCHO and HCOOH in the current ISO standard seem to be too strict. (C) 2018 The Electrochemical Society.