Application of the molecular replacement method to a heavy-atom problem

The molecular replacement method has been applied to the heavy-atom problem in a case for which a heavy-atom model existed for one crystal form, and b oth native and derivative data were available for another crystal form of t he same molecule, the absolute values of difference amplitudes for the seco nd form were used in the calculation. The key requirement for obtaining a s olution is that the contents of the asymmetric unit are the same and the sa me heavy-atom compound is used in both cases.