Sharing Variables

Question

I wonder could someone help me, I realise this problem is very basic but im new to Web Services and the whole lack of state between webmethods is catching me out. Im trying to share a variable between two web methods. Ive tried setting up a session variable from the constructor but it deosnt get changed by the method i change it with. only within that method it does, the other method that needs the input receives the value it was set up with. What is the correct way of sharing a session variable between two web methods so that it can be changed by one and this change read by the other. Thanks in advance - regards