We evaluated workers and performed an industrial hygiene assessment at a plant where raw eggs are processed into powdered egg yolk and whole egg. Egg dust levels in the packaging room straddled the American Conference of Governmental Industrial Hygienists' (ACGIH) exposure guideline of 10 mg/m3 for nuisance dust. We obtained medical histories from 25 workers, and performed physical examinations, spirometry, and serial determinations of peak expiratory flow rate (PEFR) by portable meter every 3 hrs (while awake) for 7 days. We defined symptomatic bronchial lability to be a decrement in PEFR on any one day of 20% or more of the day's maximum, with concurrent symptoms. Skin-prick tests and serum assays for specific IgE by the radioallergosorbent (RAST) method were performed to assess sensitivity to commercial egg proteins, egg protein fractions, and freshly prepared extracts of whole egg powder and yolk. We classified participants as definite cases of asthma if both the examining physician diagnosed asthma and symptomatic bronchial lability was demonstrated by serial PEFR determinations. Definite noncases of asthma were those participants in whom the physician did not diagnose asthma and in whom symptomatic bronchial lability was not demonstrated by PEFR. All five definite cases, compared to three of 16 definite noncases of asthma, had one or more positive skin-prick tests to egg proteins. Four of five cases, compared to 0 of 14 noncases, who had serum determinations, had an elevated RAST to one or more of the egg proteins. This study demonstrates that occupational asthma associated with IgE-mediated allergy to egg proteins occurs among workers exposed to inhaled egg proteins.