The paper addresses the problem of toxic emission from non-road vehicles. The paper presents the results of the investigations and analyses related to the engine operating conditions of a selected group of non-road vehicles. The presented tests have been carried out on a large groups of vehicles - several from each representative group. This was chiefly on-site construction machinery (dump tracks, excavators, bulldozers) used in the construction of the motorway and as an auxiliary equipment in an open-cast mine. An analysis has been performed based on which a range of the most frequently used loads and engine speeds was determined. The obtained time density characteristics (distribution of speeds and loads in time) of the engines was compared to the measuring points of the toxic emission homologation cycle. On this basis conclusions have been drawn in relation to the correlation between the measuring points of the cycle and the most frequently used areas of loads and speeds of different non-road vehicles. From the presented data it results that the currently applicable stationary homologation cycle does not fully reflect the areas of the most frequently used engine speeds and loads Further suggestions for the investigations and analyses have also been made in relation to the issue at hand. Besides, based on the obtained results certain proposals have been formed for further development of the non-road vehicles emission legislation.