Pollen is routinely monitored, but it is unknown whether pollen counts represent allergen exposure. We therefore simultaneously determined olive pollen and Ole e 1 in ambient air in Cordoba, Spain, and Evora, Portugal, using Hirst-type traps for pollen and high-volume cascade impactors for allergen. Pollen from different days released 12-fold different amounts of Ole e 1 per pollen (both locations P<0.001). Average allergen release from pollen (pollen potency) was much higher in Cordoba (3.9pg Ole e 1/pollen) than in Evora (0.8pg Ole e 1/pollen, P=0.004). Indeed, yearly olive pollen counts in Cordoba were 2.4 times higher than in Evora, but Ole e 1 concentrations were 7.6 times higher. When modeling the origin of the pollen, >40% of Ole e 1 exposure in Evora was explained by high-potency pollen originating from the south of Spain. Thus, olive pollen can vary substantially in allergen release, even though they are morphologically identical.