I just found some SPlus function nls2: http://www-bia.inra.fr/J/AB/nls2/welcome.html I found it mentioned in a book by Huet et al (1996), Statistical tools for nonlinear regression, Springer. I thought I would mention it here, just in case anyone was interested. I personally find nlm to be quite easy to use for nonlinear least squares as it is. Bill Simpson -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._