Mobile emission measurement systems (PEMS), according to current legal acts, can measure nitrogen oxide emission intensity using two different methods, one of which uses the chemiluminescence method and the other the ultraviolet light method. Stationary (laboratory) systems, according to the regulation, use only the chemiluminescence method. The following article analyses the results of tests obtained during WLTC tests from laboratory analysers (chemiluminescence method) with the results from two mobile analysers using nitrogen oxide analysers operating on the basis of two different methods. As a result of this analysis, the differences in the results of nitrogen oxide emissions from mobile systems compared to measurements from stationary systems in the WLTC test on a chassis dynamometer were described. The research was performed at the BOSMAL Institute of Automotive Research and Development using a passenger car equipped with a spark-ignition engine. The analysis showed differences in the results of nitrogen oxide emissions between mobile analysers for measuring nitrogen oxide emission intensity using the NDUV method and mobile analysers CLD. Measurements with mobile analysers also differ noticeably from the results obtained from stationary (laboratory) analysers. However, the greatest influence on the difference in the obtained results is the applied measurement method.