Molecular mechanisms underlying the development of androgen-insensitive prostate cancer (AIPC) are poorly understood. However, there is growing evidence that different molecular profiles may result in the development of AIPC. Cell line studies demonstrate that c-Jun and c-Fos, via formation of the transcription factor activated protein 1 (AP-1), activate androgen-regulated genes independent of androgens and that c-Jun alone acts as an androgen receptor co-factor. The aim of this study was to investigate whether increased levels of c-Jun and phosphorylated c-Jun are associated with the development of AIPC using clinical material. Material from a cohort of 51 patients with paired tumours, obtained before and after the development of AIPC, and with full clinical biochemical follow-up, was retrieved from the archives. Tumour c-Jun, activated c-Jun, c-Fos, and pan protein kinase C (PKC) protein expression were analysed by immunohistochemistry and protein expression was scored by two independent observers using a weighted histoscore. No evidence was found to suggest that c-Jun acting as an androgen receptor co-factor influences the development of AIPC. However, it was observed that patients with high expression levels of phosphorylated c-Jun had a significantly shorter survival from relapse compared with patients with low phosphorylated c-Jun protein expression (p = 0.023), suggesting that increased AP-1 levels may promote AIPC tumour growth. Whilst PKC did not appear to activate c-Jun in vivo, increased PKC expression in AIPC tumours was also associated with decreased patient survival from time of relapse (p = 0.014). In conclusion, the data support the hypothesis that activation of c-Jun plays a role in the development of AIPC via AP-1 formation in some patients. However, PKC appears to promote the development of AIPC independently of c-Jun activation via an as yet unexplained mechanism. Copyright © 2004 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.