Hi, mmCIF should be able to handle crystal structures analysed by MAD. MAD means that data of one crystal are collected at different wavelengths and so several data sets are given. Therefore, category _diffrn_radiation should provide a wavelength ID which is linked to category _reflns. Example: loop_ _diffrn_radiation.entry_id _diffrn_radiation.wavelength_id _diffrn_radiation.wavelength ZDFB51 1 0.9323 ZDFB51 2 0.9192 ZDFB51 3 0.9185 ZDFB51 4 0.8983 loop_ _reflns.entry_id _reflns.wavelength_id _reflns.number_obs _reflns.number_all ZDFB51 1 3028 11370 ZDFB51 2 3052 11598 ZDFB51 3 3054 11572 ZDFB51 4 3056 11653 Anke Gelbin