Discrepancies among different methods for assaying human growth hormone have been described in various studies. The two major sources of discordant results are the heterogeneity of the antibodies and the different standardization bases used by the assay manufacturers. We propose standardizing assays with 22-kDa biosynthetic monomer human growth hormone diluted with the diluents supplied by the kit manufacturers. In a study of two monoclonal immunoradiometric assays (Hybritech, specific for the 22-kDa monomer; Sorin, recognizing also a 20-kDa variant hormone), standardization with 22-kDa monomer human growth hormone reduced by 63% the differences in results for 44 serum samples from children. The use of 22-kDa human growth hormone as a common standard, highly pure and easily available in large quantities, could help limit the interpretative problems in growth diagnostics.