NOx emission reduction for current diesel trucks was demonstrated in on-road programs. Urea-SCR systems were installed in heavy-duty trucks (Mercedes Actros, MAN F2000) powered by 6-cylinder turbocharged and intercooled engines with 12 liter displacement (OM501LA, D2866 LF). The trucks were operated by trucking companies in typical duty. Some trucks have been operated for more than 30 in the programs to date. Current European standard grade diesel fuel with a sulfur content of max. 500 PPM was used. The reducing agent for the catalytic conversion was 32.5 wt-% urea solution. Supply logistics for urea were established for the demonstration program. The program included bench testing, chassis dynamometer test, and vehicle road test with on-board measuring as well as in-use catalyst spot check investigation. Emissions were measured upstream and downstream the exhaust gas aftertreatment system, proofing the performance of SCR technology.