How to pass a parameter with an '&' in the string using javascript?

I have a Javascript function that executes a webpage using ifrHidden.location.  Sometimes a string with an '&' is being passed into the URL, but it doesn't work with a string like that.  Is there a Javascript function that I can use to deal with this?

Thanks.

<script language="javascript" type="text/javascript">
  function jsTierChange(urlpar){
     if (urlpar == 'secondTier'){
       ifrHidden.location = 'generateSecondTierList.cfm?firstTier=' +   document.workloadrecord.selectProductListFirstTier.value;
      makeHttpRequest('selectList1.html', 'alert');
}                  
else{
      ifrHidden.location = 'generateThirdTierList.cfm?secondTier=' + document.workloadrecord.selectProductListSecondTier.value;
     makeHttpRequest('selectList2.html', 'alert');                  
}
}
</script>