This study was conducted in a microwave popcorn plant in November 2001. Of 149 current workers, 140 participated in the survey. Of the 140 participants, 32 were excluded from sputum induction: 27 subjects had medical contraindications from β-blocker use (n = 8), cardiac problems (n = 5), recent operation (n = 2), recent pneumothorax (n = 1), pregnancy (n = 2), or postbronchodilator baseline FEV1 < 60% of predicted (n = 9). Five subjects were excluded because they had worked at the plant for < 1 month. Common cold and other upper airways infectious diseases were among exclusion criteria, but according the pretest questionnaire none of the participants had any infectious diseases before starting the induced sputum procedure. Of the 108 participants undergoing sputum induction, analyzable induced sputum samples were obtained from 81 subjects. Sixteen workers failed to produce sputum, 8 subjects produced inadequate samples, and 3 workers experienced a decline in FEV1 during induction sufficient to halt the procedure. The mean age (± SD)‘ of participant workers with analyzable sputum samples was 33.8 ± 11.9 years. Forty-nine workers were male, and 38 workers reported current smoking. There were 59 workers in the high-exposure group, with a history of high flavoring exposure in mixing, microwave packaging, maintenance, and quality control. A low-exposure group included 22 workers from office, polyethylene packaging, warehouse, and outside sections of the plant. Diacetyl exposure over the preceding year for the two exposure groups differed by up to two orders of magnitude (Fig 1
). Normal control values for sputum cell counts were obtained from a previously characterized group of 24 healthy, never-smoking, nonasthmatic subjects (41.6% men; mean age, 33.8 ± 9.3 years) participating in airway research at the University of California, San Francisco.