Primary measures, to reduce the NOx emissions from diesel engines, penalize the fuel consumption and aggravate the CO2 problem. Instead, an after-treatment system is proposed that permits optimum combustion and yet reduces the NOx by more than 95%. Such installations are in operation for more than five years. Successful deployment on a short-haul ferry, subject to highly cyclic operation, began in Spring 1992. The chief features are high space-velocity (25,000 1/h), urea as non-toxic reactant and rapid transient response. The attained results counter the misgivings about the SCR catalysis. Development aims at further halving the size thus facilitating service in off-highway vehicles such as locomotives and earth-movers. The integration of particulate traps using knitted micro-fibers is under development.