Personal dust exposure levels and dust particle size distribution in the California agriculture industry were examined. Four stage cascade impactors and respirable dust cyclones were used to measure personal dust exposure levels during ground preparation, spraying, mowing, planting, cultivating, harvesting, swathing, bailing, and irrigating operations at a field crop farm; hand and machine harvesting operations at a fruit and nut farm; and milking, feeding, and manure removal operations at a dairy farm. The dust mass on the membranes and filters was analyzed gravimetrically. Median sampling time equaled 76 minutes for the cascade impactor and 87 minutes for the cyclone. Dust exposure levels measured with the cascade impactor were highest during ground preparation, feeding, planting, and mechanical harvesting operations. Dust exposure levels measured with the cascade impactor were lowest during milking. Personal dust exposure levels were reduced considerably by the presence of an enclosed tractor cabin. Most of the dust particles sampled were of the extrathoracic fraction. The mass median aerodynamic diameter for all samples averaged 49 micrometers (microm). The percentage of particles smaller than 9.8microm in diameter was higher with a cabin present than without a cabin present. Particles smaller than 9.8microm were more prevalent during dairy farming operations than during most field crop or fruit and nut farming operations. The percentage of particles smaller than 9.8microm increased with increasing log transformed dust exposure levels. Dust exposure levels measured with the respirable cyclone were highest during ground preparation, feeding, cultivating, harvesting, and mowing operations. Dust exposure levels measured with the cyclone were lowest during milking and irrigating operations. The presence of a cabin on the tractor reduced respirable dust levels considerably. The authors conclude that personal dust exposure levels are high during various operations in California agriculture.