This paper presents a study of the transient behaviour of the turbocharged engine equipped with a diesel particulate trap. The trap is considered to be placed before the turbine, to fully exploit the high regeneration potential of the turbocharged engine. This necessitates some design changes to the exhaust system in front of the turbine, in order to keep a good turbocharger response. The fast temperature response of a light-weight exhaust manifold, partially offsets the effect of the trap thermal inertia. However, the turbocharger lag may deteriorate in some cases, due to the significant modifications produced by the trap dead volume on the pulse turbocharging system operation. This effect varies with trap size and mean pressure drop, and it could necessitate a new turbocharger matching. The study, motivated by LAT experience in this field, is facilitated by use of a specially developped transient computer code which focuses on turbine operation, in order to assess the effect of trap system design. The results may be used as guidelines in the design of diesel particulate trap systems for turbocharged engined vehicles of various categories.