Male Pekin ducks adapted to seawater and maintained under sheltered conditions (27 degrees C) in the laboratory may consume considerable volumes of petroleum without showing overt symptoms of distress. Under these conditions, birds consuming petroleum-contaminated food have shown a persistent hyperphagia; this was most apparent among those given food contaminated with South Louisiana crude oil, least apparent among birds given No. 2 fuel oil, and intermediate among those that consumed food contaminated with Kuwait crude oil. When maintained at 27 degrees C, some mortality occurred among the birds given South Louisiana crude oil (22.2%) and No. 2 fuel oil (35.7%), whereas none of the freshwater- and seawater-maintained birds given uncontaminated food and none of the birds given Kuwait crude oil died during this period. Following their exposure to chronic mild cold stress (3 degrees C), mortality occurred in all groups of birds; the birds that had consumed petroleum-contaminated food tended to die earlier and in larger numbers than either the seawater- or freshwater-maintained control birds. These effects suggest that the mortality in all groups of birds was due primarily to the additive effects of a series of nonspecific stressors. Thus, at autopsy, birds that had succumbed to the effects of these stressors frequently showed adrenal hypertrophy and severe involution of the lymphoepithelial tissues. The consumption of petroleum-contaminated food seemed to constitute only one of a series of environmental stressors, and, among birds that were already exposed to stressors such as hypertonic drinking water and persistent cold, the ingestion of petroleum seemed to render them more vulnerable and death frequently ensued.