The polymerase chain reaction (PCR) technique for amplification of genomic fragments of spotted fever group (SFG) rickettsiae directly from field samples of ticks, tick ova, tick larvae, tick faeces and organs of wild mice was employed for the first time in P.R. of China. Ticks and rodents were collected in Beijing and Heilongjiang, Hainan and Hebei Provinces. The PCR primers were designed from the DNA sequence encoding the 190 K protein of R. rickettsii for a 532 bp long product. Seven of ten tick samples, three of four tick ovum samples, one of two tick larva samples, four of seven tick faeces samples (the samples represented pools of several individuals), and two of twenty-seven wild mouse organs were found PCR-positive. In comparison with PCR assay, the haemolymph test gave similar but not so clear-cut results. PCR assay is recommended as a rapid, sensitive and convenient tool for the detection of SFG rickettsiae in endemic foci. The fact that tick faeces were found to certain extent PCR-positive for the presence of SFG rickettsiae is apparently the first report on this subject and contributes to the knowledge of the transmission of these micro-organisms in the nature.