jquery ajax response from variable from a target file

[Taex]

I am sending username and password to some target file (auth.php) using jquery ajax.In auth.php file, i have many variables "var a1", "var b1".If authentication success, the variable "a1" set to pass(a1='pass').My problem is how to access the only the "a1" variable from "auth.php" using the ajax response.small code is below:\[code\]$.ajax({ url: "auth.php", type: "POST", data: "dataString", success: function (txtBack) { -- here i need to check the variable "a1" from auth.php }\[/code\]Thanks in advance.