Thirty-one workers with occupational asthma caused by snow-crab processing were assessed by a long-term follow-up on three occasions at mean ± SD intervals of 12.8 ± 5.4, 31.4 ± 6.3, and 64.4 ± 6.3 months after leaving work. The diagnosis of work-related asthma was initially confirmed in all of them by specific inhalation challenges at the workplace or by laboratory inhalation of snow-crab boiling water (n = 24) or by serial monitoring of airway caliber and bronchial responsiveness to histamine at work and off work (n = 7). Total duration of work-related exposure was 12.8 ± 5.6 months (range, 3 to 21 months), and the duration of symptoms after onset was 6.8 ± 4.2 months (range, 1 to 18 months). At the time of diagnosis, all 31 subjects required medication for asthma, 11 had a FEV₁ ⩽ 85% predicted, and all subjects had a PC₂₀ ⩽ 16 mg/ml. Twelve of 25 serum samples assessed showed high levels of specific immunoglobulin E (IgE) antibodies to crab meat and/or boiling water. At the time of the first follow-up, there was a reduction in the number of subjects still requiring medication, with a significant reduction in FEV₁, and a PC₂₀ ⩽ 16 mg/ml. However, no further change was observed afterwards. Similarly, the mean FEV₁ and FEV₁/FVC improved significantly from the time of diagnosis to the first follow-up (p < 0.01), with a plateau thereafter. The time to reach a plateau was longer for PC₂₀, as this was significantly (p < 0.05) detected only at the time of the second follow-up. Nine of 31 and five of 30 serum samples assessed at the time of the second and third follow-ups still showed high levels of specific IgE to crab meat and/or boiling water. There were significant reductions in the levels of specific IgE antibodies to crab boiling water at the time of the second and third follow-ups. A significant reduction in specific IgE antibodies to crab meat was obtained only at the final follow-up. We conclude that a plateau of improvement in occupational asthma after cessation of exposure is reached at mean intervals of 1 yr for spirometry and 2 yr for bronchial hyperresponsiveness. At these intervals, there is a concurrent reduction in the levels of specific IgE antibodies, though no plateau is generally observed.