It really doesn't matter how much gain/loss you've got out of the sale. The important thing is that cash proceed from the sale portion of the exchange shall be deposited with an intermediary, and the cash proceed from the sale portion MUST BE paid toward the exchanged property. Any left over cash that ultimately goes to you is called "boot", and may subject to the capital gain tax. It doesn't matter the left over cash is from your principle from the sold property or capital gain of the sold property. If you have boot, the boot is presumed to be capital gain and may subject to CGT.