Hi Waltenegus, you should consider to show us your code and the data you used to fit the curve. If you can't or if you prefer you can simply show the code and some sample data on which the code can be run. You'll find nice and useful tool in nlstools package. Hope this help Giuseppe ----- Giuseppe Calamita PhD at CNR-IMAA Italian National Council of Research - Institute of Methodologies for Environmental Analysis, Tito Scalo -Potenza ITALY -- View this message in context: http://r.789695.n4.nabble.com/curve-fitting-an-exponential-function-tp4644765p4645439.html Sent from the R help mailing list archive at Nabble.com.