Histoplasmin test and calcification herd of lung field were studied on the people in Okayama prefecture. And the results were as follows. 1. The positive rate was 3.9% in 2, 970 people on the observation of histoplasmin skin test in each district and it showed such a high rate of 8.4% in Mitsuishi district. 2. The positive rate was high in the miners and workers in the brickyard on the observation of professional distinction, and it showed close relation to the profession handling the ground and to the handled ground. 3. No correlation was recognized between histoplasmin and the size of induration or redness of skin reaction. and also between the induration's size of histoplasmin test and the reddend size of tuberculin skin test. 4. On the observation of lung calcification herd in each group of histoplasmin and tuberculin skin test, it showed the most high rate in the group with the positive histoplasminand negative tuberculin skin test, and the distribution of calcification herd in the lung field showed difference between the cases with the positive histoplasmin skin test and the cases with the positive tuberculin skin test and the calcification herd in the former showed a spread tendency to the lung fields. 5. The adoption of the standard being used hitherto, i. e. the size of skin induration between 5 mm and 7 mm was appropraite for the decision of positive histoplasmin skin test. According to this standard, the positive rate of histoplasmin skin test was 0.37% in Okayama prefecture.