Prostate cancer selectively metastasises to skeletal sites, where it normally produces osteoblastic lesions. This study investigated whether haematopoietic growth factors known to be present in the bone environment could be involved in the survival and proliferation of prostate skeletal metastases. To evaluate this hypothesis we investigated the effects of recombinant granulocyte/macrophage colony-stimulating factor (rGM-CSF), recombinant granulocyte colony-stimulating factor (rG-CSF), recombinant erythropoietin (rEPO) and recombinant interleukin-3 (rIL-3) on the growth of 3 human prostate cancer cell lines. Two hormone-insensitive cell lines, PC-3 and DU145, were significantly stimulated by rGM-CSF and rEPO in serum-free medium but their growth was unaffected by incubation with rIL-3 or rG-CSF. A hormone-sensitive cell line, LNCaP, was stimulated only by rGM-CSF. To investigate further the involvement of GM-CSF in prostate cancer, the presence of GM-CSF protein in the 3 prostate cancer cell lines was examined by immunohistochemistry, and analysis of cell line conditioned media was carried out by ELISA and Western blotting. These techniques demonstrated that GM-CSF-like material was produced by both DU145 and PC-3 cells but not by LNCaP. The results from ELISA found that media conditioned by DU145 and PC-3 cells contained 1.7 and 2.5 pg GM-CSF/micrograms protein, respectively, whereas no GM-CSF was detectable in the LNCaP conditioned media. Our results were also confirmed by Western blot analysis demonstrating one single band for DU145 and PC-3 conditioned media which co-migrated along with the standard rGM-CSF band. No bands were associated with the LNCaP conditioned media. The presence of GM-CSF gene transcripts in DU145 and PC-3 cells was established by reverse transcription and polymerase chain reaction of total RNA.