The use of pollen extracts in the treatment of hay-fever occasions certain demands upon the laboratory supplying this material: The solution should not be too irritating for subcutaneous administration.The solution should be the most potent possible.The solution should be stable in content of the antigenic substances. In the effort to meet these conditions many formulae have been used; but the need for stabilizing, and especially for standardizing the process has not thus far been satisfactorily solved. Heretofore, the most dependable factor for measuring the strength of a given solution has been the nitrogen content. That this can be accurately correlated with the antigenic content or with the skin reaction has been lately questioned (1), (2), (3), (4). And even if the nitrogen alone could determine the original antigenic value of a solution, it offered no further evidence as to the stability of the extract alone or as to the influence of other factors, such as preservative.