<p>Despite their potential significance, bio-ecological determinants of ethical and sustainable business behavior have been largely unexplored in business ethics research. This study examines the impact of pathogen stress—a bio-ecological factor that has been shown to be critical for human attitudes, intentions, and behaviors—on firms’ environmental sustainability practices. Pathogen stress refers to the prevalence of a broad spectrum of infectious agents, including viruses, bacteria, protozoa, and helminths, that threaten human health and survival. We theorize that higher levels of pathogen stress negatively affect firms’ adoption of environmental sustainability practices. Analyzing data from nearly 20,000 firms across 37 countries using the World Bank Enterprise Surveys and a country-level pathogen stress index, we observe that firms in contexts with higher pathogen prevalence are less likely to adopt environmental sustainability practices. To elucidate the underlying causality, we employ an experimental vignette design that identifies two mediating psychological mechanisms: a temporal mechanism (heightened short-term orientation) and a relational mechanism (increased ingroup trust bias). We discuss the implications of the results for business ethics research and suggest several future research avenues to improve the understanding of bio-ecological factors for ethical and sustainable firm decision-making, strategies, and behaviors.</p>