Abstract: The present invention relates to a process for producing microparticles laden with at least one active, wherein the microparticles are formed from a thermoplastic organic, polymeric material and in the unladen state, in their interior, have at least one cavity connected via pores to the surface of the microparticles, wherein (a) a composition of unladen microparticles are impregnated with a liquid comprising the active, whereby laden microparticles are obtained, which contain in the interior cavity the liquid, and (b) subjecting the laden microparticles to thermal treatment by passing a stream of free flowing laden microparticles in a carrier gas through a heated zone at a temperature of at least 20 K, in particular at least 40 K, e.g.