Unusual, primarily pulmonary, manifestations of hantaviral illness occurring in the southwestern United States raised the possibility of person-to-person transmission of a recently recognized hantavirus, Sin Nombre virus. To determine whether such transmission had occurred among health care workers (HCWs) exposed to patients with confirmed hantavirus pulmonary syndrome, we evaluated HCWs who had cared for patients with hantavirus pulmonary syndrome or who had processed specimens from these patients. Information about exposure to these patients and about recent illnesses was obtained via a standardized questionnaire. Serum specimens were tested for IgM and IgG antibodies to hantaviruses with use of ELISAs. Of the 396 HCWs, 266 (67%) reported that they had been exposed to patients with hantavirus pulmonary syndrome or to their body fluids or that they had processed laboratory specimens from these patients. Although 108 (27%) of the HCWs reported fever, myalgias, or respiratory illnesses during the 3 months before the serum specimens were obtained, hantavirus antibodies were not detected in any HCW. These data suggest that person-to-person transmission of Sin Nombre virus is unlikely to occur in health care settings.