Using regex to replace text with bold version - problem with case

I have a function that searches a string for supplied criteria value. I have the following string: $str = "PHP is great. Isn't php great? I like Php."; If $criteria equals PHP, Php, php (or even PhP) I want to convert $str to: <b>PHP</b> is great. Isn't <b>php</b> great? I like <b>php</b>. I've tried: 1. $str = eregi_replace("$criteria", "<b>$criteria</b>", $txt) This converts all case-insensitive occurences of "php" to the case used in $criteria. 2. $str = ereg_replace("$criteria", "<b>$criteria</b>", $txt) This only matches case-sensitive matches. 3. $criteria_2 = strtolower($criteria); $txt = ereg_replace("$criteria_2", "<b>$criteria_2</b>", $txt); $criteria_3 = strtoupper(substr($criteria,0,1)) . substr($criteria,1); $txt = ereg_replace("$criteria_3", "<b>$criteria_3</b>", $txt); This works pretty well. It matches "php" and "Php", but doesn't match anything with upper-case characters anywhere other than the beginning of the word. Is there a better way to approach this? Does anyone have a solution that works? Steven Werby {steven-lists@befriend.com}