A comparison of sub-milligram mass standards was undertaken within EURAMET between NPL (as the pilot laboratory), INM (Romania), CEM (Spain), CMI (Czech Republic), SMU (Slovakia) and NSC IM (Ukraine). The weights circulated had nominal values of 500 micrograms, 200 micrograms (2 weights), 100 micrograms and 50 micrograms. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).