use below java script for dropdown selectedIndex.
pass the object instance (eg. comboBox1.clientID) either in server side or client side and the text witch u have to select..
I think this code will help you.
Example:
<html>
<head>
<title>Customer Inquiry</title>
<SCRIPT language="JavaScript">
function setIndex(){
var obj = document.getElementById('select');
var YourText="MS"; // pass your text from here
obj.selectedIndex= getIndexOnText(obj,YourText);
}
function getIndexOnText(obj ,YourText)
{
for(i=0; i < obj .length;i=i+1){
matchText = obj .options[i].text;
if(YourText == matchText){
return i;
}
}
}
</SCRIPT>
</head>
<body>
<form name="sysaccess" >
<select name="select1" id="select">
<option value="CL">CL</option>
<option value="EL">EL</option>
<option value="PS">PS</option>
<option value="MS">MS</option>
<option value="GS">GS</option>
</select>
<input type="button" onclick="setIndex()()">
</form>
</body>
</html>