The MAXSLOPE taxometric procedure was first described in
Grove, W. M., & Meehl, P. E. (1993). Simple regression-based procedures for taxometric investigations. Psychological Reports, 73, 707-737.
A more extensive description and proofs are given in
Grove, W. M. (2004). The MAXSLOPE taxometric procedure: Mathematical derivation, parameter estimation, consistency tests. Psychological Reports, soon to appear.
MAXSLOPE-02032004.r is the latest program version. It has been run successfully on R v1.6 to 1.9.1. It may rely on various libraries being available and certain functions defined, from among the ones you'll find in the downloadable .Rprofile file; only download that file if you find you need it.
Grove (2004) mentions finding that the simple plug-in estimators of the taxon and complement class means on X and Y are biased. This "Addendum: Explanation of How Bias in Estimators of Latent Group Means is Removed" derives a set of asymptotically unbiased estimators.