autocomplete in jquery

Question

i have a textfield which has the autocomplete plugin of jquery .I am getting the json data from the PHP in the form of (ABC:BCD) what my problem is iam getting autocomplete but when i select that iam getting the value in the textfield

$("#txt1").autocomplete({
    minLength: 1,
    source:  "abc.php?searchMode=''",
    select: function(event, ui) 
    {   
        var label= ui.item.label;
        var value= ui.item.value;
        $('#txt1').val( label );

    }
});

I want to get the Label in the Text field but Iam always getting the "value" of the json key :value .I want the key in the text field