Again, it is not the deduction amount that is the question.  We agree it is fmv of the marketable security that is deductible, and it is possible that the fmv is less than the original cost., and in that case the security would be sold and the proceeds donated.   I have just never found support for the proposition that the IRS says, "if you donate the marketable security, then you don't have to also recognize the gain."  Usually, the IRS makes you recognize the gain, which then gives you basis, and that is what is written off.  I can think of no other instance where there is this exception, except in this  one instance.  I just want to know what grants this exception.