[en] Under the commission of Science and Technology Agency, Japan Chemical Analysis Center has determined the levels of strontium-90 and cesium-137 in air-borne dust samples collected in 10 prefectures throughout Japan. Dust samples were collected by the aspiration of 3000m or more air at 1.0 1.5m above the ground surface in 10 prefectural public health laboratories and institutes. The samples collected during three months (the precipitation of about 10,000m air) were combined, and were forwarded to Japan Chemical Analysis Center after carbonization. These samples were ashed in an electric muffle furnace at Japan Chemical Analysis Center. The ash to which both some carriers and hydrochloric acid were added, was destroyed under heating. The solution was dissolved into hydrochloric acid and filtered, after it was added with nitric acid and heated to dryness. The filtrate was radiochemically analyzed for strontium-90 and cesium-137. Results obtained during the period from April, 1975 to March, 1976 are shown in Table 4. And sampling locations are shown in Figure 4. (author)