Cysteine proteinases from the latex of plants of the family Caricaceae are widely used industrially as well as in pharmaceutical preparations. In the present work, a 23 kDa cysteine proteinase from Carica candamarcensis latex (designated CMS1MS2) was purified for crystallization using three chromatography steps. The enzyme shows about fourfold higher activity than papain with BAPNA as substrate. Crystals suitable for X-ray diffraction experiments were obtained by the hanging-drop method in the presence of PEG and ammonium sulfate as precipitants. The crystals are monoclinic (space group P2(1)), with unit-cell parameters a = 53.26, b = 75.71, c = 53.23 A, beta = 96.81 degrees , and diffract X-rays to 1.8 A resolution.