How can I compare two files in a batch file?

How can I compare two files in a batch file, and perform an action based on whether or not they match? I've tried something like:

if file1.txt NEQ file2.txt goto label

but it compares the actual string "file1.txt" rather than the file. I've read about the COMP command, but it doesn't seem to work if I put it in an if statement. Does anybody know how to do this? Sorry, but I rarely use batch files and have little experience in them.

Thanks in advance.