The biochemical assessment for newly recognized acromegaly is in most, but not all patients straightforward. Although significant improvements in the methods of biochemical testing for acromegaly have recently been made, major pitfalls to the assessment of this disease still exist. A number of different schemes have been employed for the assessment of GH secretion in clinical practice. Random GH levels have been often used, but remain unreliable for the assessment of acromegaly. Mean GH levels are also frequently used to assess GH status, but are not specific for the diagnosis of acromegaly. Measurement of glucose suppressed GH levels is the preferred method for assessing GH secretion in acromegaly. However, it is essential to recognize that when using highly sensitive and specific GH assays, nadir GH levels can be < 1 microg/L after oral glucose in some patients with newly diagnosed acromegaly and postoperative patients with active disease. On the other hand, when using most clinically available commercial GH assays which are less sensitive and specific than those used in research studies, failure of GH suppression into the normal range set in these studies is not alone diagnostic of active acromegaly. In order to diagnose acromegaly, documentation of GH excess should be accompanied by elevation in levels of the GH dependent peptide, insulin-like growth factor I (IGF-I). Consideration also needs to be given to the clinical context in which GH and IGF-I are being measured as both can be altered in a number of clinical settings other than acromegaly. Both IGF-I and GH evaluations are important and complimentary parts of the biochemical assessment of acromegaly.