This proposal is to perform further SANS contrast measurements on three protein/DNA interactions currently worked on at the Research Complex at Harwell. This is part of an ongoing productive relationship between the two facilities, coordinated by Dr. David Scott of the University of Nottingham funded by ISIS to sited in the RCaH 2 days a week.The systems understudy all form part of crystallographic studies as part of an MRC programme grant to Prof. Simon Phillips, the RCaH Director, and all are important in the fundamental processes of DNA repair, recombination and replication. Preliminary data is available from SAXS and analytical ultracentrifugation measurements showing that the systems are stable in D2O and monodisperse. Preliminary SANS data through SANSexpresses has shown that suitable concentration ranges are attainable for further SANS measurements.