All the experimental investigations performed in the last years on newly sold motorcycles, equipped with a three-way catalyst and electronic mixture control, clearly indicate that CO and HC cold additional emissions, if compared with those exhausted in hot conditions, represent an important proportion of total emissions. Consequently, calculation programs for estimating emissions from road transports for air quality modeling in dedicated local areas should take into consideration this effect. From this motivation, an experimental activity on motorcycles cold emissive behavior is being jointly conducted by Istituto Motori of the National Research Council (IM-CNR) and the Department of Mechanic and Energetic (DiME) of the University of Naples. The study explains a calculation procedure to model the cold start transient behavior of motorcycles; through this methodology it's possible to evaluate the cold transient duration, the emitted quantities during the cold phase and the relevant time-dependence function. This method also analyzes the influence of kinematic parameters on motorcycles emission factors during the cold-start. The whole procedure was applied to analyze the exhaust cold extra emissions of the regulated pollutants (CO, HC and NOX) for one high-performance motorcycle of 1000 cm₃ swept volume, belonging to the Euro-3 legislative category, tested on a dynamometer bench. For this motorcycle, cold-start extra emissions and transient durations depend on the pollutant and on specific driving cycles.