Human testicular germ cell tumours of adolescents and adults (TGCTs), including their precursor lesion carcinoma in situ (CIS), show expression of a 1.5 kb alternative transcript of the platelet-derived growth factor (PDGF) alpha-receptor gene. The so-called P2 promoter involved is located in intron 12 and its activity was found to be mutually exclusive with activity of the classical promoter (P1), which encodes the full-length receptor. The presence of the 1.5 kb transcript could be a putative marker for the early molecular diagnosis of TGCTs. In order to validate the RT-PCR approach, this study shows that not more than 100 transcripts are necessary to obtain positivity in the test used; moreover, samples from TGCTs or CIS-containing tissues can be diluted many-fold before resulting in false-negative findings. This study also shows that within TGCTs, as in TGCT-derived cell lines, expression of the 1.5 kb transcript is differentiation-dependent and positively correlated with expression of the embryonic transcription factor OCT-4/POU5F1. Furthermore, the results indicate that in some non-TGCT cancers and cell lines the 1.5 kb transcript is also expressed, but without concomitant OCT-4/POU5F1 expression. The 1.5 kb transcript is also present in early B cells and derived leukaemias (B-ALL). In spite of similarities in chromosomal location, down-regulation upon differentiation of TGCTs, and PDGF alpha-receptor and c-KIT (the stem cell factor receptor) both being a tyrosine kinase receptor, no correlation was found between activity of the P2 promoter of the PDGF alpha-receptor gene and expression of c-KIT. In conclusion, the 1.5 kb transcript of the PDGF alpha-receptor is expressed in various cells and tissues, including particular blood cells. Although this may hamper the use of this transcript as a marker for malignancies in general, it does not appear to interfere with assays for the early detection of TGCTs.