array_diff Computes the difference of arrays &reftitle.description; arrayarray_diff arrayarray1 arrayarray2 array ... Compares array1 against array2 and returns the difference. &reftitle.examples; "green", "red", "blue", "red"); $array2 = array("b" => "green", "yellow", "red"); $result = array_diff($array1, $array2); print_r($result); ?> ]]> Multiple occurrences in $array1 are all treated the same way. This will output : blue ) ]]> &reftitle.seealso; Two elements are considered equal if and only if (string) $elem1 === (string) $elem2. In words: when the string representation is the same. This function only checks one dimension of a n-dimensional array. Of course you can check deeper dimensions by using array_diff($array1[0], $array2[0]);. This was broken in PHP 4.0.4! &reftitle.seealso; array_diff_assoc array_intersect array_intersect_assoc