Industrial hygiene surveys were conducted at Colorado farms and elevators during the harvests and grain shipping periods of 1992 and 1993. Of the eight farms and seven elevators examined during the 1992 harvest, four farms and three elevators were resurveyed during the subsequent winter and harvest. Personal samples were obtained for total dust, respirable dust (RD), respirable silica (14808607) (RS), and microbes. Area samples were obtained for organophosphate pesticides. During the 1992 harvest, the mean total dust concentration measured at the elevators, 27.33mg/m3, was significantly higher than that measured at the farms, 8.45mg/m3. All farms and elevators exceeded the threshold limit value (TLV) for grain dust of 4mg/m3. During the 1993 harvest, the mean total dust concentrations measured at the elevators and farms were 14.16mg/m3 and 6.81mg/m3, respectively. Over the entire study, the dust levels at the elevators ranged from 4.55 to 53.67mg/m3, while the dust levels at the farms varied from 2.84 to 15.23mg/m3. The mean mass median aerodynamic diameter of dust particles was 5.94 micrometers (microm). The mean RD fraction at farms, 0.28mg/m3, was significantly less than that at elevators, 0.97mg/m3. Although the RS levels at both farms and elevators were generally low, an elevated RS level was detected in samples obtained during grain bin cleaning. Airborne pesticide concentrations did not exceed the TLV. At farms, airborne microbial concentrations usually exceeded 1x10(4)/m3, whereas at elevators, microbial concentrations exceeded 1x10(6)/m3. The quantity of viable organisms decreased significantly during wheat storage. During harvest, the fungi Alternaria-alternata and species of Cladosporium and the bacterium Enterobacter-agglomerans were the most frequently identified microbes. The authors recommend the use of respirators during grain transport, the safety training of agricultural workers, and further study in this area.