Several HPLC methods are available for the analysis of iso-alpha-acids and reduced iso-alpha-acids in hop products, worts and beers. However, the calibration of each method to a generally agreed standard has only been possible to date in the case of the iso-alpha-acids, for which purpose the purchase (from Labor Veritas, formerly VSB, Zürich) of a commercially prepared standard comprising the dicyclohexylamine ("DCHA") salts of purified iso-alpha-acids has formerly been recommended. In 1998, at the Annual Meeting of the ASBC, a paper was delivered by Dr John Paul Maye in which he described not only an improved method for the preparation of DCHA iso-alpha-acids, but also methods for obtaining pure standards for HPLC analysis of the three, commercially important, reduced iso-alpha-acids. This paper stimulated later debate, from which emerged the proposal that an international committee be formed for the purpose of first evaluating Dr Maye's methods, then moving on to the preparation of each standard type in quantity sufficient for issue as an officially approved, HPLC standard. Dr Richard Wilson was invited to form and chair this committee, bringing together suitable representatives from ASBC, EBC, IoB (now IGB) and BCOJ. Consequent to its formation, the International Subcommittee for Isomerised Hop alpha-acids Standards has worked hard to progress its mission and the new standards have now been produced and approved. They are available from ASBC and Labor Veritas (acting for EBC). These four "International Calibration Standards" are: DCHA-Iso, ICS-I1 (DCHA salts of trans- form, iso-alpha-acids); DCHA-Rho, ICS-R1 (DCHA salts of cis- form, rho-iso-alpha-acids); Tetra, ICS-T1 (Purified tetrahydroiso-alpha-acids, as mixed cis- and trans- forms); and DCHA-Hexa, ICS-H1 (DCHA salts of cis- form, hexahydroiso-alpha-acids). Each standard was evaluated for purity by HPLC, elemental analysis, melting point and UV absorption. Cohumulone ratios were also established and the long-term stability of such preparations assessed. All four standard types are considered likely to be stable in cold (freezer) storage, though DCHA-Iso may have slight instability at ambient storage temperature. An isocratic method for HPLC analysis of unknown samples (based on EBC Method 7.8) was used to finally establish purity values for each standard, and is recommended for general use. The subcommittee plans to continue its work, making checks on stability and also trying to establish in more detail the exact identity, where not already known, of each of the component compounds in these complex preparations.