Subnormal temperatures were found to depress the production of interferon by bovid herpesvirus 2 (BHV-2)-infected bovine testicular cells, bovine peripheral blood leukocytes, and bovine monocytes, as well as by BHV-2 antigen-stimulated immune peripheral blood leukocytes. Interferon titers generated at 30 degrees C were approximately 10 percent of those at 40 degrees C. Also, subnormal temperatures depressed interferon function. Bovine testicular cells treated at 40 degrees C for 24 hours with high concentrations of BHV-2-induced bovine monocyte interferon or BHV-2 antigen-stimulated immune peripheral blood leukocyte interferon, and then infected with BHV-2 and retreated with interferon at 40 degrees C, had little or no viral growth or cytopathic effect after 72 hours. Cultures without interferon, or those treated with the same amount of interferon at 30 degrees C, had significantly more cytopathic effect and had viral titers up to 10(7) TCID50 higher than cultures at 40 degrees C. Earlier in vitro studies done without exogenous interferon showed that BHV-2 replicated to high titers at 30 degrees but not at 40 degrees C. Thus, at low temperatures (30 degrees C) in vitro, BHV-2 induced little interferon, was not highly suppressed by interferon, and replicated to high titers. At higher temperatures (40 degrees C), BHV-2 replication induced high interferon levels, was strongly suppressed by interferon, and replicated poorly. This may help explain the restriction of BHV-2 lesions to skin despite the presence of virus in both skin and internal organs in infected cattle.