In regions of highly diversified agriculture, herbicides used in one field may not be compatible with crops growing in nearby fields. Injury to nontarget crops may occur from drift or localized atmospheric transport of herbicide residues. Pea, bean, and corn seedlings have been used as sentinels to detect atmospheric deposition of trace residues. Seedlings were exposed at various locations throughout south central Washington and exchanged on a weekly basis with a new set of plants. Plants were returned to a lath house and observed over 3 weeks for development of symptoms indicative of probable exposure to four classes of herbicides—sulfonylureas, phenoxyacetates, aminophosphonic acids, and bipyridiliniums. The most frequently observed symptoms on sentinel plants were chlorotic spots on the upper leaf surfaces; such symptoms were created under controlled conditions by exposing plants to aerosols of the sulfonylurea (SU) herbicide chlorsulfuron. For 3 years, the greatest incidence of probable SU symptoms was detected during April; however, occurrence of symptoms was not correlated with periods of maximum use of SU herbicides on wheat in the region. The results suggested a general atmospheric loading of herbicides with occasional deposition, rather than point source drift. Further tests are needed to quantitate the exposures of sentinel plants and determine if chlorotic spots are associated with adverse physiological effects.