The structure determination of organic compounds is desirable for the development of medicines, aroma chemicals, and agricultural chemicals. However, the crystallization of organic compounds is often troublesome, because crystallization requires a relatively large quantity of high purity compounds and crystallization trials often need to be performed repetitively using different conditions. Some proteins are known to be able to bind to various organic compounds. The multidrug-resistance regulator protein RamR is one such protein. We have developed a structure determination method for organic compounds using RamR. RamR bound to organic compounds, including one compound that was not a known ligand for RamR, and the structures of the complexes were successfully determined. Because the RamR crystal is hydrophilic, this method may be useful for compounds that cannot be handled by the crystalline sponge method. (C) 2019 Elsevier Inc. All rights reserved.