Is there any port limitation with SoftwareSerial on MEGA?

When using UNO, the SoftwareSerial can use port 2 for RX and port 3 for TX. But it does not work using the same sketch on MEGA. And I tried for a few times and found that the port 50 and 52 can be used.

So is there any limitation to choose RX and TX ports for SoftwareSerial on MEGA?

Have a look at the softwareSerial ref page - http://arduino.cc/en/Reference/SoftwareSerial

Thank you beige. I've got the answer.