Five nurses aged 31-55 years old had a history of asthmatic symptoms after being exposed to psyllium that they prepared and distributed to patients. They had been nurses for 9-20 years and had reported asthmatic symptoms related to work in the past 3-12 months. They reported symptoms of rhinoconjunctivitis and all were atopic but only one had a previous history of asthma. Four of the five tested subjects had an immediate skin reaction to a commercial psyllium extract. All had IgE antibodies to psyllium. At the time that they were investigated, four out of the five had a significant increase in bronchial responsiveness to methacholine (PC 20 less than 8 mg/ml). Inhalation challenges with psyllium caused isolated immediate (one subject) and dual reactions (three subjects). One subject exposed for only 1 min to the psyllium powder experienced a severe immediate bronchospastic reaction, which required intubation for 3 h with complete functional recovery thereafter. This experience illustrates the precautions necessary, with the inclusion of a cautious dose-response approach, even with an 'occupation-type' challenge in the laboratory.