The heterogeneity of pollen-allergic individuals is well-known but poorly characterized. Twenty-six patients were studied to characterize their immunologic and clinical patterns. Thirteen patients were allergic only to grass pollens, and 13 other patients were allergic to grass-pollen and other pollen species, including Cupressaceae, plane tree, olive, and Parietaria. The IgE response was assessed by the titration of serum total IgE and orchard grass-specific IgE, as well as by IgE immunoblots to orchard-grass pollens. Clinical reactivity was assessed by nasal challenge with orchard-grass pollens before the pollen season and nasal and bronchial symptom-medication scores between April 1 and June 15. Pollen counts were obtained during this period of survey. Polysensitized patients had significantly increased levels of serum total and specific IgE and a greater heterogeneity of IgE immunoblots, suggesting an enhanced qualitative and quantitative IgE immune response. Polysensitized patients had nasal and bronchial symptoms occurring earlier than grass pollen-allergic individuals, confirming the priming effect caused by other plans flowering with an earlier season for both nasal and bronchial mucosa. Alternatively, the early symptoms may be attributable to the tree pollens or might reflect the higher grass-pollen IgE level in the polysensitized group. Bronchial symptoms appeared a few weeks after nasal symptoms. Nasal challenges were similar in both groups, and the severity of nasal symptoms during the season was not significantly different in both groups, suggesting that the intensity of symptoms is not related to the sensitization nor to the IgE immune response of the subjects.