To examine the relationship between allergy and acute attacks of asthma, we have examined adult patients with acute asthma presenting during a defined pollen season. Sera from 59 patients presenting with acute asthma to the David Grant Medical Center emergency room at Travis Air Force Base during the spring "epidemic" of asthma were assayed for IgE antibody (Ab) to five allergens (mite, cat, cockroach, ryegrass pollen, and ragweed) with RAST. Control sera were obtained from 34 patients without asthma and 25 employees. The results demonstrate that 92% of the patients with asthma had >200 units of IgE Ab to ryegrass pollen (~20 ng of IgE Ab per milliliter) compared to 14% of the control subjects (x2 = 69; p < 0.0001; odds ratio = 69). Some of the grass pollen-allergic patients also had increased levels of IgE Ab to ragweed, but only 25% had >200 units. In contrast, there was no significant difference between subjects with asthma and control subjects in the prevalence of IgE Ab to the three indoor allergens (mite, cockroach, and cat). Twelve percent of the patients with asthma compared to 5% of the control subjects had >200 units of IgE Ab to one of these three (x2 = 0.98; p > 0.1; odds ratio = 2.5). Dust samples from the homes of 15 of the patients with asthma demonstrated very high levels of grass pollen ( 13 15 houses with >10 μg of allergen per gram of dust), low levels of mite ( 13 15 homes with <2 μg of allergen per gram of dust), and no detectable cockroach allergen. These results demonstrate that the development of IgE Ab to an inhalant allergen (i.e., grass pollen) increased the patients' odds of developing acute asthma during a period of increased exposure.