Four workers from a cedar sawmill who developed red cedar asthma are described. They had serial measurements of lung function and nonspecific bronchial hyperresponsiveness (NSBH) several years before and after the development of chest symptoms. Measurements of dust concentration and specific IgE antibodies to plicatic acid-human serum albumin (PA-HSA) conjugate were also carried out before the onset of disease. NSBH developed in parallel with the development of asthma and was not present in any of the workers beforehand, indicating that it is not a predisposing host factor. Nasal symptoms preceded chest symptoms in three workers, suggesting that this may be an early marker of the disease. Although dust concentrations for jobs located both inside and outside the sawmill were low, jobs associated with somewhat higher exposures were associated with the initiation of asthma symptoms.