Workers in the coffee industry can develop occupational allergic disease upon exposure to dust associated with coffee manufacturing. Since controversy exists as to the source or chemical nature of these allergens, the mouse model of reaginic antibody production was used to assess the potential sources of allergens in samples obtained from a local coffee manufacturing plant. Mice were immunized with extracts of coffee dust and beans and the resulting reaginic antibody response determined by the passive cutaneous anaphylaxis reaction. Cross-reacting allergens were detected in samples of coffee dust, cleaner can debris and green coffee beans, but not in chaff or roasted coffee beans. None of the allergens detected in coffee samples cross-reacted with extracts of castor beans, although these extracts contained the potent castor bean allergen. Green coffee bean allergens partially purified by gel filtration were heterogeneous with respect to molecular size, although quite similar in their reactivity with reaginic antiserum. These results suggest that the green coffee bean is the major source of allergen in coffee manufacturing plants. This allergen is heterogeneous with respect to size and heat lability, and is immunochemically different from the castor bean allergen.