If paid-in-full today October, 2008, what should be the total amount due, including a reasonable interest rate on 11 thousand dollars loaned to a friend in January, 1982, in which there was no written agreement?

This is kind of difficult because it is so simply stated. There are many kinds of loans which include many kinds of re-payment. In this case, if you want to charge a simple interest rate of 6% per year with no compounding, then you figure the orignal loan amount x 6% to get the interest per year. Then multiply the number of years since the loan origination x the interest per year to get the total interest due you. Add this to the original loan amount to get the total amount due to you. For your case, the interest per year = $660, number of years = 26, total interest = $17,160, total amount due to you = $28,160. So here's where the problem comes in: If you loaned to a friend or family member, you may be outcast if you try to collect this. If it was to someone starting a new business and they were successful, then they will gladly repay you according to some reasonable terms. How to collect then becomes the more important question. Friend/Family = don't collect interest but do collect the principal they owe you (or whatever portion you feel reasonable). Business = calculate with a competitive interest rate and offer either periodic payments on the balance or offer a "discount" if they pay you lump sum (or sums per year). Hope this helps.