Filter RelationQuery by relation_type
A RelationQuery is just an EntityFieldQuery under the hood, and since relation_type is the bundle key of the relation entity type, both

$query = relation_query('node',1234,1);
$results = $query-&gt;entityCondition('bundle', 'is_member_of')-&gt;execute();


and

$query = relation_query('node',1234,1);
$results = $query-&gt;propertyCondition('relation_type', 'is_member_of')-&gt;execute();


should work.