been added were found to be 381 nm and 398 nm respectively thus it was found that microparticles with high redispersibility were selected although a small degree of aggregation was still observed moreover the releasing behavior of aso06 and bdp in 3 bsa containing pbs was examined as a result as shown in fig6 and 7 both agents exhibited the same releasing behavior regardless whether or not a freeze drying treatment had been carried out and thus it was clarified that such a freeze drying treatment does not affect the sustained release of the agent macrophages were collected from the abdominal cavity of a mouse which had been stimulated by administration of 1 5 ml of 10 proteose peptone the collected macrophages were inoculated with a concentration of 100 000 cells 48 wells and they were then cultured in an rpmi1640 medium containing 10 fbs for several days after exchanging the medium with a fresh medium plga microparticles in which rhodamine a fluorescent dye produced by the method described in example 1 had been encapsulated as an agent model were added thereto followed by incubation at 37 u00b0 c for 1 5 hours the resultant product was washed with pes 3 times and was then left for a certain period of time thereafter the cells were immobilized with a 4 neutral formalin solution and were then observed with a fluorescent microscope ix 70 olympus as shown in fig8 as a result it was found that rhodamine encapsulated in microparticles was internalized macrophages at a higher level than a case.