diff --git a/README.rst b/README.rst
index 3e746b56..254bc8e9 100644
--- a/README.rst
+++ b/README.rst
@@ -60,14 +60,15 @@ Jedi supports many of the widely used Python features:
 - class decorators (py3k feature, are being ignored too, until I find a use
   case, that doesn't work with Jedi)
 - simple/usual ``sys.path`` modifications
+- ``isinstance`` checks for if/while
 
 However, it does not yet support (and probably will in future versions, because
 they are on my todo list):
 
-- assert / isinstance
+- operation support -> [3]\*3 etc.
 - manipulations of instances outside the instance variables, without using
   functions
-- operation support -> ``__mul__``, ``__add__``, etc.
+- assert
 
 It does not support (and most probably will not in future versions): 
 
diff --git a/jedi/dynamic.py b/jedi/dynamic.py
index 53a617f4..47316156 100644
--- a/jedi/dynamic.py
+++ b/jedi/dynamic.py
@@ -492,3 +492,43 @@ class RelatedName(BaseOutput):
 
     def __hash__(self):
         return hash((self.start_pos, self.module_path))
+
+
+def check_flow_information(flow, search_name):
+    """ Try to find out the type of a variable just with the information that
+    is given by the flows: e.g.
+    >>> if isinstance(k, str):
+    >>>     k.  # <- completion here
+
+    ensures that `k` is a string.
+    """
+    try:
+        assert flow.command in ['if', 'while']
+        assert len(flow.inits) == 1
+        ass = flow.inits[0].get_assignment_calls()
+        assert len(ass.values) == 1 and len(ass.values[0]) == 1
+        call = ass.values[0][0]
+        assert type(call) == parsing.Call and str(call.name) == 'isinstance'
+        assert bool(call.execution)
+
+        # isinstance check
+        isinst = call.execution.values
+        assert len(isinst) == 2
+        assert len(isinst[0]) == 1
+        assert len(isinst[1]) == 1
+        assert isinstance(isinst[0][0], parsing.Call)
+        # names fit?
+        assert str(isinst[0][0].name) == search_name
+        classes_call = isinst[1][0]  # class_or_type_or_tuple
+        assert isinstance(classes_call, parsing.Call)
+        result = []
+        for c in  evaluate.follow_call(classes_call):
+            if isinstance(c, evaluate.Array):
+                result += c.get_index_types()
+            else:
+                result.append(c)
+        for i, c in enumerate(result):
+            result[i] = evaluate.Instance(c)
+        return result
+    except AssertionError:
+        return []
diff --git a/jedi/evaluate.py b/jedi/evaluate.py
index e5d4a9e0..b14a09f6 100644
--- a/jedi/evaluate.py
+++ b/jedi/evaluate.py
@@ -1118,10 +1118,11 @@ def get_scopes_for_name(scope, name_str, position=None, search_global=False,
                 result.append(par)
             return result, no_break_scope
 
+        flow_scope = scope
         result = []
         # compare func uses the tuple of line/indent = line/column
         comparison_func = lambda name: (name.start_pos)
-        for scope, name_list in scope_generator:
+        for nscope, name_list in scope_generator:
             break_scopes = []
             # here is the position stuff happening (sorting of variables)
             for name in sorted(name_list, key=comparison_func, reverse=True):
@@ -1136,7 +1137,7 @@ def get_scopes_for_name(scope, name_str, position=None, search_global=False,
                     else:
                         result += r
                     # for comparison we need the raw class
-                    s = scope.base if isinstance(scope, Class) else scope
+                    s = nscope.base if isinstance(nscope, Class) else nscope
                     # this means that a definition was found and is not e.g.
                     # in if/else.
                     if result and not no_break_scope:
@@ -1147,10 +1148,19 @@ def get_scopes_for_name(scope, name_str, position=None, search_global=False,
             if result:
                 break
 
-        if not result and isinstance(scope, Instance):
+            while flow_scope and flow_scope.isinstance(parsing.Flow):
+                result = dynamic.check_flow_information(flow_scope, name_str)
+                if result:
+                    break
+                flow_scope = flow_scope.parent()
+            flow_scope = nscope
+            if result:
+                break
+
+        if not result and isinstance(nscope, Instance):
             # getattr() / __getattr__ / __getattribute__
-            result += check_getattr(scope, name_str)
-        debug.dbg('sfn filter "%s" in %s: %s' % (name_str, scope, result))
+            result += check_getattr(nscope, name_str)
+        debug.dbg('sfn filter "%s" in %s: %s' % (name_str, nscope, result))
         return result
 
     def descriptor_check(result):
diff --git a/test/completion/isinstance.py b/test/completion/isinstance.py
new file mode 100644
index 00000000..db0a4e4f
--- /dev/null
+++ b/test/completion/isinstance.py
@@ -0,0 +1,19 @@
+if isinstance(i, str):
+    #? str()
+    i
+
+if isinstance(j, (str, int)):
+    #? str() int()
+    j
+
+while isinstance(k, (str, int)):
+    #? str() int()
+    k
+
+if not isinstance(k, (str, int)):
+    #? 
+    k
+
+while not isinstance(k, (str, int)):
+    #? 
+    k