help with preg_match

Hi, I'm trying to write a function that validates the input in a textarea. I just want to allow alphanumrical characters, and if the user enters anything else, I display an error message by calling error(). But the following doesn't work. Even if I enter "hello" in the textarea, I get the error message. What am I missing? // validate entered text in textarea function validate_textarea($unchecked_text) { if (!preg_match ("/^[a-zåäö0-9]$/is", $unchecked_text)) { error("You have used unlegal characters, just alphanumeric is ok."); } } Best regards, Anders