Poly(N-isopropylacrylamide) (PNIPA) and Poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPA-co-AA)) microgels loaded with 5-aminolevulinic acid (ALA) were prepared by the spray-drying method. The amount of drug loaded was 290 mu g ALA/mg microgel for PNIPA and 244 mu g ALA/mg microgel for P(NIPA-co-AA) microgels. Maximum in vitro drug release took place within 15-30 min for PNIPA and 1-1.5 h for P(NIPA-co-AA) microgels as a function of pH, at 37 degrees C. Transdermal delivery from microgels showed permeation fluxes 10 times higher than the passive diffusion flux. The cytotoxicity of microgels synthesized in HeLa cells after the application of photodynamic therapy (PDT) was superior compared with the administration of ALA in solution alone. Finally, the use of these microgels as a delivery vehicle for ALA constitutes a system capable of enhancing its topical administration and PDT effectiveness.