The availability of the Tropheryma whipplei genome offers the putative possibility of choosing logical DNA targets. We applied a PCR assay (targeting repeated sequences of T. whipplei) to samples from patients with Whipple's disease and to those from members of a control group. When compared to the results seen with regular PCR, the sensitivity of repeat PCR was significantly enhanced (P = 0.02) without alteration of its specificity.