This paper presents a new system to produce micrometric narrow size distribution particles. The principle is the same as for a conventional supercritical antisolvent process (SAS), with the contact of the organic solution containing the solute to be precipitated and the supercritical CO2 playing the role of an antisolvent. This paper exposes the functioning of the system used for the contact of the two phases. It is constituted by two concentric tubes; an external one partially for the CO2 and an internal one for the organic solution. Its name is the Concentric Tube Antisolvent Reactor (CTAR). This system is a compacted and simple one. It has been tested with a usual polymer (L-poly lactic acid) often processed by the use of the SAS methods. Different experiments have shown that this system is convenient for the production of particles, leading to almost equivalent results as in other processes with identical operating conditions. There are still remaining problems for the recovery of the powder formed, which is usual for this kind of process. This system could be very useful for the scaling up of the process, by multiplying the number of tubes with an easy permanent control on the operating conditions. Some improvements have been made for operating parameters, as the concentration of LPLA in the organic solution and the molar ratio sol vent/supercritical CO2 that can be processed. (c) 2006 Published by Elsevier B.V.