Possible Duplicate:
Setting the column gap in a twocolumn document
How can I change the distance of two columns in a two-column document?
Possible Duplicate:
Setting the column gap in a twocolumn document
How can I change the distance of two columns in a two-column document?
Here is the internal definition of \twocolumn. In this definition you can see all length which are use.
\def \twocolumn {%
\clearpage
\global\columnwidth\textwidth
\global\advance\columnwidth-\columnsep
\global\divide\columnwidth\tw@
\global\hsize\columnwidth
\global\linewidth\columnwidth
\global\@twocolumntrue
\global\@firstcolumntrue
\col@number \tw@
\@ifnextchar [\@topnewpage\@floatplacement
}
Taken from latex.ltx
You are looking for \columnsep.