I'm using etags for the first time in a long while, and it has an infinite loop buffer-tag-table-list. tags-check-parent-directories-for-tag-files is at its default setting of t so etags goes up the parent directories as expected. It does this by running (expand-file-name ".." cur). When cur is "/", (expand-file-name ".." cur) returns "/..". Then (expand-file-name ".." cur) returns "/" and we continue around again. Perhaps the check should look for cur equal to "/" and stop? (What about Windows machines?) Ray