Four laboratories, Institut Francais du Petrole (IFP), PSA Peugeot-Citroen, Renault, and Union Technique de l'Automobile, du Motocycle et du Cycle (UTAC), have conducted an interlaboratory test to evaluate the performances of the condensation particle counter (CPC). The technical program was based on tests carried out on four passenger cars, one gasoline and three diesel ones, tested on the New European Driving Cycle (NEDC). The regulated pollutants are also measured, as indicators of test repeatability and good working conditions. The 1.96RSD reproducibility values of the total particle number determined by CPC on NEDC are 87, 58, 41, and 220%, respectively, for the Euro4 gasoline, Euro3 diesel, Euro4 diesel, and Euro3 diesel plus DPF (diesel particulate filter) vehicles. The CPC repeatability and reproducibility are poorest at lower particle numbers. The CPC performances, in terms of reproducibility, are comparable but generally not much better than the reproducibility of particulate matter emissions determined by the gravimetric method.