The rapidly evolving discipline of environmental endocrinology is briefly reviewed from the 'heroic era' to the present. Environmental endocrinology has developed in response to the need to understand how hormones modulate and control physiological processes in animals exposed to the exigencies of their particular, natural, environment. This has only been made possible through spectacular developments in hormone assay techniques which now make feasible hormone measurements on microlitre volumes of body fluids. The results of some recent research programmes working on animals in the field are reviewed. These include the reproductive responses of migratory birds in the Arctic, the role of antidiuretic hormone in the survival of desert rodents and marsupial wallabies, some interesting behavioural effects of glucocorticoids in reptiles, and the dynamic interplay between hormones and social status in primates.