The author studied the distribution of the Paragonismus westermani in Ehime prefecture of Japan; at first the intracutaneous reaction was performed on 51865 students or pupiles of primary, junier and senier high school; final examination such as sputum examination, feces examination, chest X-ray were performed on the skin reaction-positive persons; examination of metacercaria in the crab, Composcia retusa, distribution in the dog were also studied. The rusults are briefly summarized as follows: 1) Of 51865 persons tested, the intracutaneous reaction revealed 3032 positive cases (3.9%), 1252 males (4.7%) and 780 females (3.0%). The positive cases vised with the rise of age; 3.7% in primary school pupils, 3.6% in junior high school students, 5.0% in senior high school students and 7.7% in adults. 2) Of 3032 skin reaction-positive cases, paragonismus westermani egg was positive in 405 cases (13.4%). The positive cases of parasite egg decreased with the rise of the age. 3) Of 405 parasite egg positive cases (72.3%) had chest X-ray findings. In about 80% of them, the pathologic shadow appeared in the middle or lower pulmonary area. 4) Further study revealed that the patient group had eaten. morecrabs, Camposicia retusa, and has more chances to contact the crab than the femele. 5) The comparative examination on subjective symptomes between the patient and heathy groups revealed a significant difference. 6) Of 909 crabs tested, 444 (48.9%) had metaceraria. The metacercaria-containg percentage was parallel to the positive rate of skin reaction. 7) Paragonismns westermani was proved in the lung of 13 (2.6%) of 482 dogs tested. This rate was parallel to that of positive skin reaction and to that of metacercaria containing in crabs.