Dear all, I am trying to fit a lme of the form: m=lme(y~F*x-1, random=...,data=...) F is a 2-level factor since I need the fixed part to differ for 2 groups. The random part depends on subgroups G. I would like to have a random effect only on the slope and I cannot figure out how to formulate the random part. If I write it like : F*x-1|G, I get random effect on both the slope and the intercept. If I use: F-1|G, the random effect is on the intercepts. If I use x-1|G I get an effect only on the slope corresponding to one of the levels of F. The coefs in the fixed part look like: F1 F2 x F1:x What kind of contrasts should I use and how can I get a random effect only on both slopes? Thank you! Irene