Sending multiple variables to AJAX... Newbie question

Hi - This is my code for the HTML

	</center><div style="margin-left:660px";><img src="images/hdr_paymentcodes.png" width="439" height="43" /></div>
	<form name="UID" action="./pmta.php" method="post" onsubmit="return formCheck6(this);">
	<table Border=0 width=30% align=center cellpadding=5 class="text">
	<input type="hidden" name="process" value="process">
	<tr><td>Location:</td><td><select name="loc" id="loc" onblur="getPayment(this.value)" >
	<?
    $b = 0;
    while ($b < count($siteadmin)) {
        if ($loc == $siteadmin[$b]) {
            echo "<option SELECTED value=\"" . $siteadmin[$b] . "\">" . $siteadmin[$b] . "</option>";
        }
        else {
            echo "<option value=\"" . $siteadmin[$b] . "\">" . $siteadmin[$b] . "</option>";
        }
        $b = ++$b;
    }
    ?>
	</select></td></tr>
	<tr><td>Payment Code ID:</td><td><input name="pmtid" id="pmtid" style="text-transform: uppercase;" class="DefaultEntry" type="text" maxlength="12" size="20" id="f1" onkeypress="return handleEnter(this, event);" onblur="getPayment(this.value)" value="<? echo $_POST['pmtid']; ?>"></td></tr>
	<tr><td>Name:</td><td><input name="pname" id="pname" style="text-transform: propercase;" class="DefaultEntry" onkeypress="return handleEnter(this, event);" type="text" maxlength="45" size="20" value="<? echo $_POST['pname']; ?>"></td></tr>
	<tr><td>Active:</td><td><select onkeypress="return handleEnter(this, event);" name="pactive" size=1>
	<? if ($_POST['pactive'] == "Y") { echo "<option value=\"Y\" selected=\"yes\">Yes</option>"; } else { echo "<option value=\"Y\">Yes</option>"; }
	if ($_POST['pactive'] == "N") { echo "<option value=\"N\" selected=\"yes\">No</option>"; } else { echo "<option value=\"N\">No</option>"; }
	?>
	</td></tr>
	</table>
	<center><input type="image" name="submit" class="submit" value="submit" id="submit" src="images/btn_addpmt.png" width="183" height="53" border=0></center>

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Here is my AJAX script

function getPayment(str) {
    if (str=="") {
	  return;
	}
	if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari
	    xmlhttp=new XMLHttpRequest();
	}
	else {// code for IE6, IE5
	  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
	}

	xmlhttp.onreadystatechange=function() {
	  if (xmlhttp.readyState==4 && xmlhttp.status==200) {
	    var my_array = xmlhttp.responseText.split("|"); // split by |
	    if (my_array[1] == null) {
            document.getElementById("submit").src = "/ef/images/btn_addpmt.png";
            document.getElementById("submit").disabled = false;
            return;
	    }
        else {
            document.getElementById("submit").src = "/ef/images/btn_addpmtfail.png";
            document.getElementById("submit").disabled = true;
  		    alert("Duplicate Payment Code found.  Please try again.");
        }
	  }
	}

    xmlhttp.open("GET","./inc/getPayment.inc.php?q="+str,true);
	xmlhttp.send();
}

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and the getPayment.inc.php (minus the connection string, etc)

$result = mysql_query($sql);

if($row = mysql_fetch_array($result))
  {
	echo $row['userid'] . "|" . $row['realname'];
  }

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My question is how do I send the variables loc and pmtid both to the ajax script?  The loc select will always have something populated in it.

Thanks for your help!
Zack