Current asthma is often excluded by the presence of normal bronchial hyperresponsiveness. We report two asthmatic patients with normal bronchial hyperresponsiveness and one asthmatic patient with mild bronchial hyperresponsiveness (methacholine PC₂₀; 24 mg/ml) which was presumed to be caused by sensitization and exposure to Black GR, the most frequent sensitizer among reactive dyes. They all complained of lower respiratory symptoms after work as well as at the workstation. The bronchoprovocation test with Black GR revealed isolated immediate bronchoconstrictions in all 3 patients and all had high specific IgE antibodies to Black GR-human serum albumin conjugate. After one worker continued at work for 3 days, he experienced a marked drop of methacholine PC₂₀, and it returned to the pre-exposure level during 1 week. The other patient whose initial methacholine challenge was negative developed bronchial hyperresponsiveness on the first day after the dye bronchoprovocation, and returned to normal bronchial hyperresponsiveness on the third day. These findings suggested that patients with occupational asthma caused by reactive dye may not always have bronchial hyperresponsiveness to methacholine, and the screening program utilizing methacholine challenges may not always identify these patients.