Work in agriculture is associated with exposure to respiratory biohazards. The most important airborne substances include grain dust and its constituents, bacteria and metabolites (endotoxin), fungi and metabolites (glucan), and storage mites. The degree of dysfunction in exposed persons depends on the biological potency and concentration of exposure as well as on individual susceptibility. Airborne contaminants frequently occur in concentrations and compositions that challenge the defence mechanisms of the lung. This may be of particular importance in the case of susceptible workers and minors, whose exposure by the virtue of family-type operations is difficult to avoid. Epidemiological and clinical studies have contributed to the identification of associations between respiratory disorders and agricultural exposures. Chronic bronchitis, asthma, hypersensitivity pneumonitis, organic dust toxic syndrome and chronic airflow limitation have been found to occur in agricultural workers. Clinical and experimental studies have advanced the understanding of immunologic and non-immunologic mechanisms involved in respiratory responses to a wide spectrum of inhaled organic dusts. Although the evidence has provided substantial insight into the occurrence and pathogenesis of respiratory disorders in agriculture, further investigation is necessary. There is a need for research involving accurate assessment of exposures and their respiratory effects. There is also a need for the establishment of preventive programs, with emphasis on reduction of harmful exposures. Increasing concern about respiratory disorders in agriculture justifies further scientific effort in both areas.