BACKGROUND Bacillary angiomatosis is characterized by vascular lesions, which occur usually in patients infected with the human immunodeficiency virus (HIV). A newly described gram-negative organism, Rochalimaea henselae, has been associated with cutaneous bacillary angiomatosis, but no organism has been isolated and cultivated directly from cutaneous tissue. METHODS We used two methods to isolate the infecting bacterium from four HIV-infected patients with cutaneous lesions suggestive of bacillary angiomatosis: cultivation with eukaryotic tissue-culture monolayers and direct plating of homogenized tissue onto agar. The patients' blood was cultured with the lysis-centrifugation method. Isolates recovered from skin and blood were identified by sequencing all or part of the 16S ribosomal RNA gene amplified with the polymerase chain reaction. RESULTS R. quintana, historically known as the agent of trench fever, was isolated from cutaneous lesions in three patients, after tissue homogenates were cultivated with endothelial-cell monolayers; R. henselae was isolated from a cutaneous lesion in one patient. In two patients, R. quintana was isolated from both cutaneous tissue and blood; in one patient it was also isolated from bone. CONCLUSIONS In bacillary angiomatosis, either of two species of rochalimaea--R. quintana or R. henselae--can be isolated from cutaneous lesions or blood, providing an additional method of diagnosis.