Index: test/unit/attributes.js
===================================================================
--- test/unit/attributes.js	(revision 6340)
+++ test/unit/attributes.js	(working copy)
@@ -354,3 +354,22 @@
 	ok( c.has(x, "hi"), "Check has1" );
 	ok( c.has(x, "bar"), "Check has2" );
 });
+
+test("radioClass(String)", function() {
+	expect(8);
+	var lis = jQuery('#listWithTabIndex li'),
+		li = lis.eq(0).radioClass("test");
+	ok( li.is(".test"), "Check that first li has class" );
+	ok( !lis.not(":eq(0)").is(".test"), "Check that siblings do not have class" );
+	li = lis.eq(1).radioClass("test");
+	ok( li.is(".test"), "Check that first li has class" );
+	ok( !lis.not(":eq(1)").is(".test"), "Check that siblings do not have class" );
+	
+	var els = jQuery('#listWithTabIndex li, #foo p'),
+		first = els.filter(":first-child").radioClass("test"),
+		last = els.filter(":last-child");
+	ok( first.is(".test"), "Check that first-child has class" );
+	ok( !els.not(":first-child").is(".test"), "Check that siblings do not have class" );
+	ok( last.radioClass("test").is(".test"), "Check that last child has class" );
+	ok( !els.not(":last-child").is(".test"), "Check that siblings do not have class" );
+});
Index: src/attributes.js
===================================================================
--- src/attributes.js	(revision 6340)
+++ src/attributes.js	(working copy)
@@ -148,6 +148,13 @@
 			// toggle whole className
 			this.className = this.className || classNames === false ? "" : jQuery.data( this, "__className__" ) || "";
 		}
+	},
+
+	radioClass: function( classNames ) {
+		jQuery.className.add( this, classNames );
+		jQuery.each( jQuery.sibling( this.parentNode.firstChild, this ), function() {
+			jQuery.className.remove( this, classNames );
+		});
 	}
 }, function(name, fn){
 	jQuery.fn[ name ] = function(){