Edmund Pellegrino has argued that the dramatic changes in American hea
lth care call for critical reflection on the traditional norms governi
ng the therapeutic relationship. This paper offers such reflection on
the obligation to ''do no harm.'' Drawing on work by Beauchamp and Chi
ldress and Pellegrino and Thomasma, I argue that the libertarian model
of medical ethics offered by Engelhardt cannot adequately sustain an
obligation to ''do no harm.'' Because the obligation to ''do no harm''
is not based simply on a negative duty of nonmaleficence but also on
a positive duty of beneficence, I argue that it is best understood to
derive from the fiduciary nature of the healing relationship.