Longstaff(l992) and Edleson, Fehr, and Mason (1993) examine option val
ues implicit in callable Treasury bonds and report a significant puzzl
e: implied option values are frequently negative. Using an alternative
approach, we reexamine this issue and find that implied option values
are generally positive, and, in contrast to previous studies, instanc
es of option values sufficiently negative to overcome the bid-ask spre
ad are rare. We explain the findings in other studies by showing that
the method used may lead to the appearance of a negative option value
when the true value is positive.