  In this paper, the existence of subharmonic solutions for a class of
non-autonomous first-order Hamiltonian systems is investigated. We also study
the minimality of periods for such solutions. Our results which extend and
improve many previous results will be illustrated by specific examples. Our
main tools are the minimax methods in critical point theory and the least
action principle. {\bf Key words.} Hamiltonian systems. Critical point theory.
Least action principle. Subharmonic solutions.
