./configure issue- no lex?

Hi all, pls help. I have first time encounter the above mentioned issue in php installation in Linux. ================================================ checking whether ln -s works... yes checking for flex... no checking for lex... no ./configure: flex: command not found checking for flex... lex checking for yywrap in -ll... no checking lex output file root... ./configure: lex: command not found configure: error: cannot find output from lex; giving up ========================================================================= i'm doing ./configure with:- ./configure --prefix=/usr/local/php-4.0.4pl1 --exec-prefix=/usr/local/php-4.0.4pl1 --with-mysql --with-xml --enable-track-vars --disable-debug --with-pgsql --with-apache=/usr/include any clues? Thanks. -- Regards. Jason Benedict Low ***One's success is not because of oneself but is given by others****