SOAP Client addHeader Problem

Hello, I want to include a SOAP_Header with every request sent to the server. I am using the addHeader-method of my SOAP_Client. This works great for the very first call but then on a second call the header is not sent again. To my understanding, the SOAP_Header should be included in every call made by the client and not just the first one. $client = new SOAP_Client(); $header = new SOAP_Header(); $client->addHeader($header); $client->call(....); // Header is sent $client->call(....); // Header is not sent ???? Any idea how to have the header sent on every call? Thanks, Martin