To determine the role of Bartonella (formerly Rochalimaea) species and Afipia felis in cat scratch disease (CSD), two polymerase chain reaction (PCR) hybridization assays were developed to detect DNA from these organisms. These assays were applied on 89 pus aspirates from skin test-positive CSD patients (group 1) and on 137 pus and lymph node specimens from CSD suspects (group 2). Bartonella DNA was detected in 96% of the samples from group 1 patients and in 60% of group 2 samples; however, A. felis DNA could not be detected in any clinical samples. These results suggest that CSD is caused by bartonellae and that A. felis does not play a significant role in this zoonosis. A strong correlation between Bartonella PCR positivity and Bartonella henselae antibody titer was found. Comparison of CSD skin test results with those obtained by Bartonella PCR suggests a low sensitivity of the skin test.