diff --git a/lib/engine.js b/lib/engine.js
index 327b8f9..a69f1a6 100644
--- a/lib/engine.js
+++ b/lib/engine.js
@@ -68,7 +68,31 @@ var sendResponse = function(jDoc, myRes, ip, bid, callback, gzip) {
 		
 		var responseHeaders = {'Content-Type': responseType, 'vary': 'Accept-Encoding', 'max-age': jDoc.secleft, 'cache-control': 'public, max-age='+jDoc.secleft+', no-transform', "Expires": jDoc.expires, "Last-Modified": jDoc.lastModified};
 		
-		doc = JSON.stringify(jDoc);
+		var ext = bid.match(/\.[\w]+$/);
+		if (ext && (ext = ext[0])) {
+			// When the bid has an extension, we only return the first api.
+			var first = _.find(jDoc, function(api, key) {
+				return api && api.cname;
+			});
+			doc = first.result;
+			
+			switch (ext) {
+				case ".kml":
+				case ".xml":
+					// When expecting response is KML or XML, we set the correct Content-Type
+					// and wrap it with quotes if it's a JSONP request.
+					responseHeaders['Content-Type'] = 'text/xml';
+					callback && (doc = "'"+ doc+"'");
+					break;
+				case ".json":
+					// Content-Type for JSON is already set above.
+					doc = JSON.stringify(doc);
+				default:
+					break;
+			}
+		} else {
+			doc = JSON.stringify(jDoc);
+		}
 		
 		if (callback) {
 			doc = callback + '(' + doc + ');';