Several reports suggest that the canonical nuclear factor-kappaB (NF-kappaB) pathway is constitutively activated in a subset of prostate cancer cells. However, except for RelA (p65), little is known about the status of NF-kappaB transcription factors in prostate cancer tissues. To clarify the status of NF-kappaB subunits, we analysed the expression and subcellular localisation of RelA, RelB, c-Rel, p50, and p52 on tissue array sections containing respectively 344, 346, 369, 343, and 344 cores from 75 patients. The subcellular localisation of NF-kappaB factors was tested against relevant clinical parameters (preoperative prostate-specific antigen, pathological stage, and postoperative Gleason grade). With the exception of c-Rel, each subunit was detected in the nucleus of cancer cells: significant nuclear expression of RelB, RelA, p52, and p50 was seen in 26.6, 15.6, 10.7, and 10.5% of cores, respectively. Surprisingly, cores expressing both nuclear RelA and p50 canonical pathway proteins were less frequently observed than cores expressing other subunit combinations such as RelB-p52 and RelA-RelB. In addition, the nuclear localisation of RelB correlated with patient's Gleason scores (Spearman correlation: 0.167; P=0.018). The nuclear localisation of both canonical and noncanonical NF-kappaB subunits in prostate cancer cells suggests for the first time that different NF-kappaB pathways and dimers may be activated in the progression of the disease.