What's the best network traffic sniffer to extract SOAP envelope information?

I need to make a bridge between two medical record systems inside my hospital (inside the firewall). One of them I’m very familiar with, but the other I am not. The vendor tells me that the system communicates from client computers to the server via SOAP.
I have used network traffic sniffers to isolate the address and port that information is being sent to, but I cannot get the packet info.