AbstractNeurotrophin‐3 (NT‐3) has been crystallized in 2 forms. Orthorhombic crystals, space group P21212, diffracted to 2.8 Å and have cell dimensions a = 39.1 Å, b = 54.0 Å, and c = 65.5 Å. The second form is space group P43212, with cell dimensions a = b = 67.1 Å, and c = 107.9 Å. The tetragonal crystals diffract to 2.8 Å at room temperature and 2.5 Å at −100 °C. The unit cell dimensions change significantly upon freezing, a = b = 66.1 Å, and c = 102.8 Å. Phases for the orthorhombic form were obtained by molecular replacement using nerve growth factor as the search model. A partially refined model of the NT‐3 dimer (75% complete) was then oriented and positioned in the tetragonal cell.