We have shown that the Lyme disease spirochete, B. burgdorferi, can invade peripheral blood fibrocytes, a CD4-, CD8-, and CD14-leukocyte sub population, with the potential to target connective tissue., The ability of fibrocytes to secrete type I collagen and to recruit and activate T cells suggests that they play a critical role in certain connective tissue disorders. We recently obtained blood from a patient of Dr. Williams with a history of documented severe fatigue syndrome (by CDC guidelines) as well as EIA and Western blot positivity for B. burgdorgeri (IgG) in blood and cerebral spinal fluid samples. Because of the patient's potential exposure to B. burgdorgeri we investigated their fibrocytes for evidence of spirochete invasion. Electron microscopic examination showed no evidence of spirochetes within this patient's peripheral blood-fibrocytes when compared to normal individuals. Despite the lack of evidence for B. burgdorferi, we found doughnut shaped, retrovirus-like particles within fibrocytes containing numerous vacuoles. Viroids were found in large, dilated cisternae of the endoplasmic reticulum which permeated the entire cell body except for the area around the nucleus. Such a foamy' appearance is characteristic of Spumaviruses. 'Foamy' viruses are highly cosmopolitan viruses which can infect CDl4+ monocytes, and CD4+/CD8+ leukocytes, but their role in human disease remains controversial. Here, we show for the first time the infection of fibrocytes by foamy' viruses, but it remains to be seen if presenting symptoms of this patient are associated with the presence of the foamy virus-like