Monoclonal antibodies against major rye-grass pollen allergens have been used to detect cross-reactive determinants in other grass pollen extracts. Antibody binding was detected by the dot blotting immunoassay in which alkaline phosphatase-conjugated anti-mouse IgG was used as secondary antibody. Taxonomically ordered variations were found between pollen of 22 grass species representing all major natural groups. One of the antibodies, that bound to the 28 to 30Kd allergen, showed high species specificity; immunoblotting showed binding to similar polypeptides in Festuca elatior but to none of the other grasses tested. This simple assay has applications in standardizing grass pollen extracts.