Abstract: In the spring of 2012, a year after the Fukushima Daiichi nuclear disaster, radiocesium-contaminated Japanese cedar pollen may have caused internal exposure to the general population by inhalation. To determine if pollen had been contaminated through uptake of radiocesium by Japanese cedars and was therefore contributing to inhalation doses, the authors measured radiocesium and Japanese cedar pollen adhered to masks worn by 68 human subjects residing in eastern Japan, including Fukushima prefecture, for 8 wk in the spring of 2012. The maximum cumulative 137Cs and 134Cs radioactivities on masks worn by an individual were 21 ± 0.36 Bq and 15 ± 0.22 Bq, respectively, and the estimated effective dose during the 8 wk was 0.494 μSv. The average estimated effective dose during the 8 wk was 0.149 μSv in Fukushima prefecture and 0.015 μSv in other prefectures, including Tokyo metropolitan. The correlation between radiocesium activity and the Japanese cedar pollen count was moderate. However, imaging-plate and light microscopy observations showed that the main source of radiocesium adhered to masks was fugitive dust.