By establishing sensitive nested reverse transcription-PCRs for the detection of mRNA of alpha-fetoprotein (AFP) and beta human chorionic gonadotropin (betahCG), we investigated the presence of circulating tumor cells in the peripheral blood of 119 patients with germ-cell tumor. A total of 336 blood samples obtained before and during therapy were examined with regard to clinical applicability. The overall ratio of positive PCR results was 26.5% and was independent of the serum concentration of AFP and hCG/betahCG. No correlation of the positivity for AFP-mRNA to serum AFP level was found. In contrast, positive results in betahCG-PCR were twice as frequent in patients with elevated serum hCG/betahCG levels as in those with normal serum hCG/betahCG levels (P = 0.012). To develop a valid correlation to tumor stage, tumor histology, and serum level of tumor markers, a subgroup of 36 patients was evaluated before definite therapy. The subgroup revealed an overall ratio of 33.3% positive PCR results. The serum level of both of the markers did not correlate with the detection of corresponding mRNA in peripheral blood samples. However, positive betahCG-PCR results were found exclusively in patients with elevated serum hCG/betahCG (6 of 18 versus 0 of 18; P = 0.019). Patients with stage IIC/III germ-cell tumor demonstrated nearly twice the frequency of positive PCR results as patients with stage I tumor [7 (41.2%) of 17 versus 4 (23.5%) of 17] in this subgroup. With regard to histology, positive PCR results were found mostly in embryonal carcinoma.