Sorry for the lengthy series of comments/questions, but writing and testing moderately complicated functions really highlights the interaction of various commands. In this particular case, the issue is generated by the following script function panel_foo(series y, list X) series lunit=$unit genr time genr ltime=time setobs 1 1 --cross-section # Define sample to exclude missing values for either y or X list vars = y X smpl ok(vars) --restrict ... smpl full setobs lunit ltime --panel-vars return matrix result end function This seemed to work fine, until I tried the following test smpl id < 10 --restrict matrix res=panel_foo(y, X) at which point the function fell over at the final setobs, reporting missing values for the panel variables. Now I understand what has happened. The "smpl full" command in the function has overridden the restricted sample that was given to the function and reverted to the full sample of data that gretl has been given. As a result, lunit and ltime, which were created within the function, have missing values for observations that were not given to the sample. I can get round this in part by defining lunit & ltime as arguments of the function and changing the calling script, but the sample restriction would still be overridden. It seems to me that the operation of "smpl full" is contrary to the principle that all operations within a function are - or should be - local. In other words, issuing the "smpl full" command within a function should do no more than revert to the data that was supplied to the function. Gordon