The authors found that the use of asthma medication among elementary schoolchildren was associated with particulate pollution (particulate matter < 10 microm in aerodynamic diameter [PM10]) in a locale where PM10 consisted primarily of coarse fraction material derived from road sanding and reentrained volcanic ash. School nurses' records in 12 neighborhood schools located close to an ambient air monitoring station were abstracted, and the numbers of oral and inhaled doses of asthma medication given daily over a period of 2.5 yr were calculated. Time-series regression models, adjusted for autocorrelation, were developed, with temperature, time trend, day of the week, and month as additional variables. Regression models were estimated, and a lagged moving average of PM10 for 7, 14, 21, and 28 days was used. All models showed positive and significant coefficients for PM10 during periods when asthma medication was administered to the schoolchildren. However, the 21-day moving average was the best fit to the model.