X-PLOR is available directly from the author (Department of Molecular Biophysics and Biochemistry, Yale University, P.O. Box 6666, New Haven, CT 06511, USA; phone: 203 432-6143; fax: 203 432-6946) for nonprofit (``academic") users and from Molecular Simulations, Inc. (16 New England Executive Park, Burlington, MA 01803-5297; phone: 617 229-9800; fax: 617 229-9899)
for all users. X-PLOR is currently used by several thousand researchers in over 500 laboratories worldwide.