text: BACKGROUND: Pecan tree pollen is considered to be highly allergenic. However, no specific scientific data about its role in causing allergic diseases are available. OBJECTIVE: To study the role of pecan tree pollen in the development of allergy. METHODS: The presence of pecan tree pollen was determined by weekly and monthly counting of airborne grains. The incidence of pecan tree pollen atopy and clinical manifestations were studied in 395 participants, aged 4-70 years, who comprised 78.2% of the whole eligible population of a rural community. The participants were skin tested for different extracts of allergens, completed detailed questionnaires, and their medical files were evaluated. RESULTS: During May, pecan tree pollen grains comprised 70% of the total airborne grains. A positive skin-prick test (SPT) to pecan was shown by 46 (11.6%) participants, constituting 25.4% of the atopic population. Of those who were found atopic to one or more allergens 50.3% had symptoms, whereas the parallel figure for those atopic to pecan pollen was 76.1% (P < 0.005); 58.7% of the pecan atopic participants had hay fever, 43.5% had asthma, and 31.5% had both hay fever and asthma. Among pecan atopic participants the incidence of hay fever increased with age (P = 0.05), while the incidence of bronchial asthma, as a sole manifestation of allergy, decreased in the > 17-year-old age group (P < 0.01). Of the pecan atopics 65.2% had clinical symptoms coinciding only with the pecan pollen season and an additional 10.9% had perennial symptoms. CONCLUSION: Pecan tree releases highly allergenic pollen grains, which are correlated to the incidence of hay fever in the exposed population. The contribution of pecan tree pollen to the symptoms was highly significant after discounting olive and cypress trees that also pollinate in the spring. In children, the pecan tree constitutes a possible etiologic agent for the development of asthma.