Something

<script type="text/javascript" language="javascript">
function GetSample()
{
	// Тут создаем соединение.
	var xmlHttp = false;
	try { xmlHttp = new ActiveXObject("Msxml2.XMLHTTP"); }
	catch (e) {
		try { xmlHttp = new ActiveXObject("Microsoft.XMLHTTP"); }
		catch (e2) { xmlHttp = false; }
	}
	if (!xmlHttp && typeof XMLHttpRequest != 'undefined') xmlHttp = new XMLHttpRequest();

		var ownership_inputs = document.getElementsByName("ownership");
		var ownership = 0;
		var ownership_input_len = ownership_inputs.length;
		for (var i = 0; i < ownership_input_len; i++) {
			if (ownership_inputs[i].checked)
			{
				ownership = ownership_inputs[i].value;
				break;
			}
		}

		var patient_inputs = document.getElementsByName("patient");
		var patient = 0;
		var patient_input_len = patient_inputs.length;
		for (var i = 0; i < patient_input_len; i++) {
			if (patient_inputs[i].checked)
			{
				patient = patient_inputs[i].value;
				break;
			}
		}

		region = document.getElementById('sample_region').value;
		specialty = document.getElementById('sample_specialty').value;
		
			str = "clinic/ajax_sample.php?";
			if(region>0) str = str+"region="+region+"&";
			if(specialty>0) str = str+"specialty="+specialty+"&";
			if(ownership>0) str = str+"ownership="+ownership+"&";
			if(patient>0) str = str+"patient="+patient+"&";
			

			if (region>0)
			{
			// Тут его используем.
			xmlHttp.open("GET", "clinic/ajax_city.php?region="+region, false);
			xmlHttp.send(null);
		
			// Получаем ответ.
			document.getElementById('city').innerHTML = xmlHttp.responseText;

			city = document.getElementById('sample_city').value;
			if(city>0) str = str+"city="+city+"&";
			}
			alert(str);
			
		// Тут его используем.
	
		xmlHttp.open("GET", str, false);
		xmlHttp.send(null);
	
		// Получаем ответ.
		document.getElementById('clinic_all_result').innerHTML = xmlHttp.responseText;
}
</script>