Limitations of file() (and serialize(), unserialize())

Hi, just wondering if there are any limitations as to the size of a line that file() can read. I have a file into which I serialize an entire data structure. It looks like it finally got too big and file() returned false. Or maybe it was the unserialize() that returned false? What are the limitations of serialize and unserialize? Thanks! Keith P.S. Just to clarify, my web host (very unfortunately) is still running v4 RC1. I tried the same code with the same data locally (using 4.0.2) and it worked. However, this has me wondering if I'll run into this problem again at a later date, or was the problem I ran into with RC1 simply limited to that version and not likely to occur again with a non-beta version? Thanks again.