A hormone profile differentiates persons with CFS versus those suffering from major depression (versus reactive depression).
It's fairly accepted that patients with major depression have higher cortisol levels and patients with CFS have lower cortisol levels.
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The following are examples from government
websites - National Institutes of Health, Surgeon
General's Office & Center for Disease Control -
better examples are available but this at least
backs up this statement:
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AS PER NATIONAL INSTITUTES OF HEALTH WEBSITE:
http://www.nimh.nih.gov/events/prosteo.cfm

"Although its causes are unclear, major
depression is associated with hormonal
abnormalities. ... higher cortisol levels, often
found in depressed patients, ..."
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AS PER SURGEON GENERAL'S WEBSITE:
http://www.surgeongeneral.gov/libra...pter3/sec5.html

Biological Factors
"Some of the core symptoms of depression, such as
changes in appetite and sleep patterns, are
related to the functions of the hypothalamus. The
hypothalamus is, in turn, closely tied to the
function of the pituitary gland. Abnormalities of
pituitary function, such as increased rates of
circulating cortisol and hypo- or
hyperthyroidism, are well established
features of depression in adults (Goodwin &
Jamison, 1990)"
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AS PER CENTER FOR DISEASE CONTROL:
http://www.cdc.gov/ncidod/diseases/cfs/info.htm

C. Hypothalamic-Pituitary Adrenal (HPA) Axis
"Multiple laboratory studies have suggested that
the central nervous system may have an important
role in CFS. Physical or emotional stress, which
is commonly reported as a pre-onset condition in
CFS patients,
activates the hypothalamic-pituitary-adrenal
axis, or HPA axis, leading to increased release
of cortisol and other hormones. Cortisol and
corticotrophin-releasing hormone (CRH), which are
also produced during the activation of the HPA
axis, influence the immune system and many
other body systems. They may also affect several
aspects of behavior.
Recent studies revealed that CFS patients often
produce lower levels of cortisol than do healthy
controls. Similar hormonal abnormalities have
been observed by others in CFS patients and in
persons with related
disorders like fibromyalgia. Cortisol suppresses
inflammation and cellular immune activation, and
reduced levels might relax constraints on
inflammatory processes and immune cell
activation. As with the immunologic data, the
altered cortisol levels noted in CFS cases fall
within the accepted range of normal, and only the
average between cases and controls allows the
distinction to be made. Therefore, cortisol
levels cannot be used as a diagnostic marker for
an individual with CFS.
A placebo-controlled trial, in which 70 CFS
patients were randomized to receive either just
enough hydrocortisone each day to restore their
cortisol levels to normal or placebo pills for 12
weeks, concluded that low levels of cortisol
itself are not directly responsible for symptoms
of CFS, and that hormonal replacement is not an
effective treatment."