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We examined C-banded karyotypes of six species of lung flukes from Japan and Korea; diploid and triploid Paragonimus westermani, P. miyazakii, P. ohirai, P. iloktsuenensis and P. sadoensis, with special reference to their karyotypic diversification. C-band analysis between the diploid and the triploid westermani revealed that two of three homologues of the triploid resembled those of the diploid in C-band pattern, while the remaining chromosome showed a different pattern from any species examined here. This karyological evidence indicates that the triploid is allotriploid probably induced by interspecific hybridization between the diploid westermani and an unknown species; we, therefore, suggest that the triploid westermani is an independent species and synonymous with P. pulmonalis (Miyazaki 1978). As the morphologically similar three species, ohirai, iloktsuenensis and sadoensis, had the same C-band polymorphism in chromosome No. 4, these species are classified as the local races of P. ohirai. Paragonimus miyazakii has one common C-band (5q) with the diploid westermani, but other bands (1q, 4q, 6q, 7p and 7q) are different. From these observations, the six species examined are phylogenetically divided into three groups: (1) westermani group containing diploid and triploid (= pulmonalis) species, (2) miyazakii and (3) ohirai including two geographic races, iloktsuenensis and sadoensis.