Michael, I'm also playing with the nls function trying to get it to work with a Gaussian. My lines that I have at the moment and I hope will help you are class(fo <- (x ~ (A/(sig*sqrt(2*pi)))* exp(-1*((bin-mu)^2/(2* sig^2))))) nls.AB <- nls(fo,data=freq.tab, start= list(A=0.1*len, mu=0.01, sig=0.5), trace=TRUE) So first I create the eq to put into the nls function, my var are the freq.tab which is a list of some binned frequency into 0.1 units and the len is amount of features in the data. I'll say quickly that at the moment I am getting a 'singular gradient error'. I hope that this helps. Cheers. Paul Benton Research Technician Mass Spectrometry o The / o Scripps \ o Research / o Institute [[alternative HTML version deleted]]