Receptors for granulocyte colony-stimulating factor (G-CSFRs) have been confirmed on the cell surfaces of several non-haematopoietic cell types, including bladder cancer cells. This observation has naturally led to the hypothesis that the expression of G-CSFR on these cells may enhance their growth by G-CSF. In this study, the expression of G-CSFR was determined in both established human bladder cancer cell lines and primary bladder cancers. We studied five different human bladder cancer cell lines (KU-1, KU-7, T-24, NBT-2 and KK) and 26 newly diagnosed bladder tumours. G-CSFR mRNA expressions on cultured cell lines were determined using the reverse transcriptase polymerase chain reaction (RT-PCR) method. Furthermore, the G-CSFR binding experiments on the cultured cell lines were conducted using the Na(125)I-labelled G-CSF ligand-binding assay method. Moreover, the G-CSFR mRNA expressions on primary bladder tumour specimens were assessed using the in situ RT-PCR method. Three out of the five cultured cell lines (KU-1, NBT-2 and KK) exhibited G-CSFR mRNA signals when the RT-PCR method was used. The G-CSFR binding experiments showed an equilibrium dissociation constant (K[d]) of 490 pM for KU-1, 340 pM for NBT-2 and 103 pM for KK cells. With in situ RT-PCR, the tumour cells of 6 out of 26 primary bladder tumour specimens (23.1%) presented positive G-CSFR mRNA signals. Thus, in this study, G-CSFR expression was frequently observed on bladder cancer cells. Therefore, the clinical use of G-CSF for patients with bladder cancer should be selected with great care.