Since it sounds like the money your parents gave to you for education, was not a personal loan with signed paperwork and repayment schedule, then they gave you a gift and now you are now just gifting them back. A returned favor wouldn't qualify as a loan but as long as you aren't over your lifetime gift amount you won't be taxed on the 50k, but you will want to file the gift form with your taxes. The bank will handle anything required for the large transfer amount, you can always inquire about your states laws with the bank first, but usually it's just paperwork they do, and that's usually it. I am not a tax professional, but I've read a lot on this subject for my own situation. If anything I've said is incorrect feel free to enlighten me. The IRS can also inform you on the matter just by calling them too!
