Infection with human parvovirus B19 induces a biphasic disease. The initial phase has been associated with viremia. During the second phase of the disease, a spectrum of clinical syndromes can manifest, including erythema infectiosum, perinatal complications, and symmetric arthropathy that resembles rheumatoid arthritis. Although investigators have suspected that some of the second-phase symptoms are related to immune complex formation, the pathogenesis of parvovirus B19-induced clinical manifestations is not understood. Herein we describe a 63-year-old woman with malaise, fever, and symmetric polyarthritis who had IgM antibodies specific for parvovirus B19. Messenger RNA (mRNA) specific for interleukin (IL) 1 beta, IL 6, and interferon-gamma (IFN-gamma) was detected by polymerase chain reaction. Transcript concentrations were semiquantified by serial dilution of cells and determination of the minimal number of cells that provided a positive signal. Concentrations of IL 1 beta and IL 6 mRNA in peripheral blood mononuclear cells collected during acute disease were increased by the factor of 32 and 8, respectively. IFN-gamma was detected at a 16-fold increased concentration. Two months later, after the patient had experienced complete recovery, production of monokines and IFN-gamma was almost normalized. These data raise the possibility that acute parvovirus B19 infection is characterized by a widespread and systemic activation of monocytes, T cells, and natural killer cells. The correlation of increased cytokine mRNA levels and clinical symptoms suggests a potential role of proinflammatory monokines and lymphokines in disease manifestations.