The aim of this study was to measure personal dust exposure levels and the dust particle size distribution during various agricultural operations in California. Personal dust exposure levels were measured with four-stage cascade impactors and respirable dust cyclones during field crop, fruit and nut farming, and dairy operations at three farms. Altogether, 103 cascade impactor measurements and 108 cyclone measurements were taken. High personal dust exposure levels were measured during various operations in particular during ground preparation operations such as land planing (geometric mean [GM] = 57.3 mg/m3, geometric standard deviation [GSD] = 2.4) and discing (GM = 98.6 mg/m3, GSD = 2.9). Dust particles were relatively large and the great majority belonged to the extrathoracic fraction. Dust levels were considerably lower when an enclosed cabin was present on the tractor; for example, during discing, dust exposure levels were reduced more than sixtyfold for the larger dust particle fraction and more than fourfold for the respirable dust fraction.