We criticize and generalize some properties of Nother charges presented in
a paper by V. Iyer and R. M. Wald and their application to entropy of black
holes. The first law of black holes thermodynamics is proven for any gauge
-natural field theory. As an application charged Kerr-Newman solutions are
considered. As a further example we consider the (1 + 2) BTZ black hole sol
ution. (C) 1999 Academic Press.