Camptothecin (CPT)-loaded nanoparticles were prepared using poly(dl-lactic acid) (PLA) and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) copolymer (PEG-PPG-PEG), and examined for particle characteristics, in vitro release, pharmacokinetics and efficacy. The preparative condition, in which the ratio of PLA/PEG-PPG-PEG/CPT was 35/35/4 (w/w/w) and organic solvent (dichloromethane) was evaporated from the emulsion at 18 degrees C, gave the nanoparticles with the diameter of approximately 230nm, fairly high drug content (ca. 1.6% (w/w)) and stable entrapment of the drug, which were used for in vivo studies. After i.v. administration to normal rats, the nanoparticles showed slightly smaller AUC but much larger MRT as compared with CPT solution, and delivered the drug greatly to the surrounding tissues, in particular to the liver. When antitumor effect was examined by i.v. administration to mice bearing sarcoma 180 (S-180) solid tumor, the nanoparticles showed a significant suppression of tumor growth without body weight loss, and their effect was better than that of CPT solution. The PLA/PEG-PPG-PEG nanoparticles were considered potentially useful to enhance the efficacy of CPT, to which the high drug retention in the body and gradual drug release appeared to be importantly related.