<i>Background:</i> Group 1 allergens elicit a specific IgE response in about 90% of grass pollen-allergic patients. The aim of this work was to study the antigenic similarity among group 1 allergens from different grasses and to develop a monoclonal antibody (MAb)-based quantitation ELISA. <i>Methods:</i> Twenty specific MAbs were produced from BALB/c mice immunized with natural Phl p 1. These MAbs were tested for specificity with thirteen different grass pollen extracts from the Poaceae family and in cross-inhibition experiments for the binding of Phl p 1. Purified group 1 allergens from Poeae grasses <i>(Dactylis glomerata</i>, <i>Lolium perenne</i>, <i>Festuca pratensis</i> and <i>Poa pratensis)</i> were tested for parallelism in quantitation ELISA. <i>Results:</i> Eighteen to nineteen anti-Phl p 1 MAbs recognized the homologous allergen in pollen extracts from grasses of the Poeae tribe. In contrast, only four MAbs recognized group 1 from <i>Cynodon dactylon</i> and <i>Phragmites communis</i>. Four groups of MAbs with different epitope specificity were identified. A grass group 1 quantitation ELISA was developed using a mix of three MAbs on the solid phase and a polyclonal rabbit antibody as the second antibody. The group 1 content could be measured in different batches of <i>Phleum pratense </i>as well as in pollen extracts from Poeae grasses, since they showed parallel dose-response curves. <i>Conclusions:</i> MAbs produced in this work enabled us to show the high antigenic similarity between group 1 allergens from temperate grasses. The results prove the usefulness of the ELISA method developed for standardization of grass allergen products.