diff --git a/gogole/query/boolean_query.py b/gogole/query/boolean_query.py
index ed7565dceb909e2fd90de832570d20d9a39afcb7..12703161d33e135b5bcdfca6293795ff710712a2 100644
--- a/gogole/query/boolean_query.py
+++ b/gogole/query/boolean_query.py
@@ -3,18 +3,36 @@ from gogole.query import Query
 class BooleanQuery(Query):
     OPERATOR_AND = ' and '
     OPERATOR_OR  = ' or '
-    OPERATOR_NOT = ' not '
+    OPERATOR_NOT = 'not '
 
     def search_documents(self, query):
          # Assume the expression
         # is in the conjunctive normal form
 
+        last_doc_id = self.collection.indexer.count_documents-1
+
         and_queries = query.split(self.OPERATOR_AND)
         doc_ids_by_conjunction = list()
 
         for and_query in and_queries:
-            doc_ids = set.union(*(self.collection.indexer.token_lookup(token) for token in and_query.split(self.OPERATOR_OR)))
-            doc_ids_by_conjunction.append(doc_ids)
+            doc_ids_disjonction = set()
+            for query_term in and_query.split(self.OPERATOR_OR):
+                query_term = query_term.strip()
+
+                is_not_query = query_term.startswith(self.OPERATOR_NOT)
+
+                if is_not_query:
+                    query_term = query_term[len(self.OPERATOR_NOT):]
+
+                doc_ids = self.collection.indexer.token_lookup(query_term)
+
+                if is_not_query:
+                    doc_ids_disjonction.update(set(range(last_doc_id)) - doc_ids)
+                else:
+                    doc_ids_disjonction.update(doc_ids)
+
+
+            doc_ids_by_conjunction.append(doc_ids_disjonction)
 
         return set.intersection(*doc_ids_by_conjunction)