ABSTRACT:In response to questions about the effects of military use of fog oil (FO) obscurant smoke, the sensitivity of cell-mediated constituents of the immune system to FO smoke was tested using an avianpox challenge in red-winged blackbirds. Although immunosuppression has been observed in seabirds that have ingested petrochemicals, the immune response in blackbirds exposed to airborne FO was not compromised. The incidence and severity of disease was somewhat less and recovery more advanced in the FO-exposed blackbirds than in controls. Circulating antibody titers to sheep red blood cells were measured in house sparrows by hemagglutination titration. No differences in total, 2-mercaptoethanol-sensitive, or 2-mercaptoethanol-resistant antibody titers were observed, suggesting that humoral immunity is also unaffected by high field-typical FO exposure. Total and differential white blood cell counts were not depressed and spleen mass and structure were not affected in any of the birds exposed to the airborne FO, further indicating that the smoke did not compromise the nonspecific immune function of the birds. No FO-induced mortality, organ pathology, or end point metabolites were observed in either passerine species. These data indicate that the use of FO at normal field concentrations is unlikely to result in decreased immunological fitness of exposed birds. DISCLAIMER:The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.