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From March 1985 to March 1989, pneumomagnetic field strength (PMFS) was measured in 579 healthy subjects who lived in areas where there was substantial road dust pollution. In response to the government's campaign to eliminate the use of studded tires, suspended road dust produced by studded tires during the snowy season in the downtown areas of Sendai, Japan, decreased from 191 micrograms/m3 in March 1985 to 116 micrograms/m3 in March 1989. Suspended road dust in nonpolluted areas varied from 11 to 15 micrograms/m3. Road dust retained in the lungs, which contained 3% iron, was magnetized from the surface of the chest wall, and the PMFS was measured. The proportion of subjects with an abnormally high initial PMFS at the first measurement was 7 to 15% from 1985 to 1989; however, the PMFS of subjects who had an initially high PMFS decreased during each succeeding year. These findings suggest that, despite a government campaign to eliminate studded tires, road dust pollution is still being inhaled by the residents.