Analysis and characterization of data from twinned crystals

It is difficult but not impossible to determine a macromolecular structure using X-ray data obtained from twinned crystals, providing it is noticed an d corrected. For perfectly twinned crystals, the structure can probably onl y be solved by molecular replacement. It is possible to detect and characte rize twinning from an analysis of the intensity statistics and crystal pack ing density Tables of likely twinning operators and some examples are discu ssed here.