Pru p 3 is a lipid transfer protein (LTP) that has been identified as the major peach (Prunus persica) allergen. However, little is known about the amount present in both raw and processed foodstuffs. Moreover, the in vivo release upon consumption of peach-containing foods remains unclear. We have developed a sensitive monoclonal antibody-based ELISA for Pru p 3. The method has been applied to measure the allergen levels in foodstuffs and the allergen release under different physiological conditions. A significant variability in all raw peaches and peach-containing foods tested has been detected. The allergen was extracted more efficiently at a low pH, and it was highly resistant to pepsin. This ELISA will be very useful in controlling the allergen concentration in diagnostics, in evaluating threshold levels in provocation tests, and in detecting hidden allergens in processed foods and cosmetics.