Heads-up: in the gretl 1.9.13 release (coming shortly) I'm reversing the preference order between gtk 2 and gtk 3. Up till now we have "preferred" gtk 2, but now that gtk 3 is mature we'll switch. That is: 1) If both gtk 3 and gtk 2 are present and no relevant option is given to ./configure, gretl will be built against gtk 3. 2) If you have both and prefer using gtk 2, you should give the option --enable-gtk2 3) If you only have gtk 2, no problem, it'll get used. However, note one thing: if you're using gtk 3 you'll also need version 3.0 of gtksourceview (for syntax highlighting). Allin