Hi , I am using nls(formula) where formula is y~ _expression y is 1 character ~ is 1 character now i have an _expression that is greater tha 502 characters. but R does not recognize anything greater than 502 characters. (Note the _expression itself is created using paste and as.formula commands) Does anyone have a suggestion. (BTW i have checked my formula and its right in case you have doubts about its length) Thanks. Harsh --------------------------------- [[alternative HTML version deleted]]