Proliferative activity was measured in 165 paraffin-embedded prostatic carcinomas using DNA flow cytometric analysis of the S-phase (SPF) and G2/M-phase fractions and CAS 200 image analysis of the proliferating cell nuclear antigen (PCNA) expression defined immunohistochemically by PC10 and 19A2 monoclonal antibodies. No significant associations were found between the flow cytometric and the two immunohistochemical measures of cell proliferation. Of the four indices, only SPF, S + G2/M, and immunostaining with 19A2 antibody were associated with the poor histological grade of the tumour. High SPF and S + G2/M were significantly associated with poor 10-year overall survival (P < 0.001) and prostatic carcinoma-specific survival (P < 0.01). Multivariate analyses of prostatic carcinoma-specific survival in patients with non-metastatic disease (M0-stage) indicated that only S + G2/M, T-stage, and histological grade (only if re-evaluated by a single pathologist) had independent prognostic significance. High-level PCNA staining (> 16 per cent of cells stained) with 19A2 antibody was associated with poor prognosis only in univariate analysis, and PC10 immunostaining had no prognostic value. In conclusion, a high proliferative activity as defined by flow cytometric S+G2/M is an independent predictor of poor survival in patients with non-metastatic prostatic carcinoma. PCNA immunostaining from formalin-fixed, paraffin-embedded prostatic carcinomas has little, if any, prognostic value.