  We compute the unknotting number of two infinite families of pretzel knots,
$P(3,1,\dots,1,b)$ (with $b$ positive and odd and an odd number of 1s) and
$P(3,3,3c)$ (with $c$ positive and odd). To do this, we extend a technique of
Owens using Donaldson's diagonalization theorem, and one of Traczyk using the
Jones polynomial, building on work of Lickorish and Millett.
