This volume is the sixth annual report and presents full summaries of 37 final reports from contracts, sponsored under the Agency's Research Contract Programme, which were completed during 1965. Including these, a total of 136 summaries have been published in the various fields in which support is provided under the IAEA Research contract program. In every case the summary of the contractor's final report has been prepared by that member of the Agency's scientific staff who has been most closely connected with the particular branch of research concerned. The scientific data are the responsibility of the contractor, though the Agency is responsible for any additional observations. The reports presented are related to research in the field of radioactive waste management and environmental sciences; health physics and radiation protection; radiobiology; safeguards methods; nuclear reactors physics and nuclear fuels; radioisotope applications in agriculture, medicine and hydrology.