Often, as environmental endocrinologists, we observe animals in nature with the goal of describing their normal endocrinology. However, the contamination of virtually all natural habitats by chemicals of anthropogenic origins (e.g., PCBs, organochlorines, phytoestrogens, alkyphenols, heavy metals) that might alter endocrine conditions suggests we need to reevaluate many of our field studies with respect to points of reference or controls. The impaired response of the stress axis of feral brown trout, Salmo trutta, correlated with chronic exposure to heavy metals is examined as a case in point although the problems extend to other hypothalamic axes as well. Our studies emphasize that measurement of one static endocrine parameter to assess the health of any hypothalamus-pituitary axis (e.g., plasma cortisol levels to indicate stress) should not be used as a biomarker for field studies.