The crystal structure of a bifunctional inhibitor of alpha-amylase and trypsin from the seeds of ragi (Indian finger millet, Eleusine coracana Gaertneri) has been determined by an X-ray diffraction method. The inhibitor consists of 122 amino acids with five disulfide bridges and belongs to the plant alpha-amylase/trypsin-inhibitor family. This is the first crystal structure determination of a member of this family. The protein, purified from the seeds of ragi, has a molecular mass of 13300 Da with a pI of 10.3. Crystals were grown by a microdialysis method using ammonium sulfate as precipitant. The improved purification protocol and the modified crystallization conditions enabled reproducible growth of the crystals. The cell parameters are a = 41. 2, b = 47.4, c = 55.9 A. The intensity data were collected to 2.9 A resolution, and the crystal structure was determined using the molecular-replacement method. The structure was refined using the X-PLOR and CCP4 program packages to a conventional R factor of 21%. The structure contains four alpha-helices between residues 19-29, 37-51, 56-65 and 90-95, and two short antiparallel beta-strands between residues 67-70 and 73-75.