This cytokine receptor binds an important cytokine involved in diverse cellular regulatory activity. The structure will help understanding the cytokinefs related cellular activity and perhaps able to modulate this activity. Crystals have been grown in a tetragonal space group with cell edges 50 x 50 x 300 A. Crystals are very radiation sensitive, and current freezing techniques have caused some kind of disorder in the lattice. Two hour exposures on a rotating anode give diffraction data up to 3.5A. It is expected that better than 3A data can be obtained at the APS.