A polymerase chain reaction (PCR) assay was designed to amplify DNA from Rochalimaea henselae, Rochalimaea quintana and Afipia felis in the purulent material from lymph nodes in three patients with clinical cat-scratch disease (CSD) and two patients with lymphadenitis from other causes. All of the patients with CSD had positive immunofluorescent antibody serology for R. henselae, while none of the controls was positive. PCR amplification confirmed the presence of R. henselae DNA and the absence of R. quintana and A. felis DNA in the purulent material from CSD patients. PCR samples from control patients were negative. The PCR amplification of R. henselae DNA was performed quickly and with great sensitivity and specificity. It confirmed the presence of R. henselae in the CSD patients and eliminated the need for more extensive diagnostic and therapeutic procedures.