Spermidine and spermine are ubiquitous polyamines which are intensely metabolised in the prostate. Polyamines are involved in the processes of proliferation and differentiation of normal and neoplastic cells. As the erythrocyte levels of these polyamines are correlated with the intratumoral levels, we assayed EPA in 45 controls, 66 patients with benign prostatic hypertrophy and 100 patients with prostatic cancer. Erythrocytic polyamines are markers of proliferation and prostatic metastases and can be used to distinguish between hormone-sensitive and hormone-resistant patients. Although non-specific, polyamines constitute circulating markers of the state of tumour proliferation of a given patient and definitely have a prognostic value which needs to be evaluated by further studies.