Hi, In Order Restricted Statistical Inference by Robertson et al (Chapter 1) there is an algorithm for isotonic regression with two or more independent variables. Has this been implemented anywhere in R? Thanks, Nathan Nathan Leon Pace, MD, MStat University of Utah Salt Lake City, UT 84132 Office: 801.581.6393 Fax: 801.581.4367 Cell: 801.205.1019 Pager: 801.291.9019 Home: 801.467.2925 [[alternative text/enriched version deleted]]