I have installed tcl/tk 8.4 . When I install ns2 or otcl with ./configure. the error occure: checking for tcl.h... -I/usr/include/tcl8.4 checking for tclInt.h... no checking for libtcl8.4.. . -L/usr/lib - ltcl8.4 checking for init.tcl... /usr/lib/tcl8.4 checking for http.tcl... /usr/lib/tcl8.4/http1.0 checking Tcl http.tcl library... yes checking for tclsh8.4... /usr/bin/tclsh8.4 configure: error: Installation of tcl seems incomplete or can't be found automatically. Please correct the problem by telling configure where tcl is using the argument --with-tcl=/path/to/package (perhaps after installing it), or the package is not required, disable it with --with-tcl=no. zhihang@ubuntu :~/ns2/otcl-1.11$ -- Best Regards zhihang wang