A commercially available enzyme-linked immunosorbent assay was used to quantitate cotinine, a nicotine metabolite, in the plasma of caged birds exposed to environmental tobacco smoke. Birds in smoking households were found to have significantly higher plasma cotinine levels (4.3–37.8 ng/ml) than control birds from nonsmoking households (0–3.6 ng/ml) (P < .001). These high levels of cotinine are similar to those reported in humans with clear evidence of clinical alteration and resultant disease from environmental tobacco smoke.