best way todo a case insensitive str_replace

Hi all. What is the best way to do a string insensitive replace? Currently I am doing: $replace = "g r"; $arr = explode(" ",$replace); $text = "PHP is GreaT!"; for($i=0;i<count($arr);$i++){ $text = str_replace(strtolower($arr[$i]),"<b>".strtolower($arr[$i])."</b>",$text); $text = str_replace(strtoupper($arr[$i]),"<b>".strtoupper($arr[$i])."</b>",$text); } Works except for "Ph","PhP","gr" etc... I am looking for suggestions before using str_split(); because my $replace string can be a bit large :) Thanks in advance. Pedro.