The cytotoxicity of a commonly used material to alleviate the symptoms of benign prostatic hyperplasia (BPH), Saw Palmetto Berry Extract (SPBE), was examined as neat oil using a set of prostatic cell lines; 267B-1, BRFF-41T and LNCaP. Proliferation of these prostatic derived cell lines is inhibited to different degrees when dosed for 3 days with SPBE. The amount of SPBE required to inhibit 50% growth (IC50) of these cell lines was 20–30 nl equivalents of SPBE per ml of medium for cell lines 267B-1 and BRFF-41T and approximately 10-fold more for the LNCaP cell line. The effect of SPBE dosing on these cell lines is not irreversible, since a 30 min treatment with SPBE at an IC50concentration does not inhibit their growth. Normal prostate cells were inhibited by 20–25% when grown in the presence of 200 nl SPBE equivalent per ml media. Growth of other non-prostatic cancer cell lines, i.e. Jurkat and HT-29, was affected by approx. 50% and 40%, respectively. When LNCaP cells were grown in the presence of dihydrotestosterone and SPBE, the IC50concentration decreased significantly compared to LNCaP cells grown in the presence of serum and SPBE. Reduced cellular growth after SPBE treatment of these cell lines may relate to decreased expression of Cox-2 and may be due to changes observed in the expression of Bcl-2. Expression of Cox-1 under similar conditions is not affected because of its constitutive expression. Since increased Cox-2 expression is associated with an increased incidence of prostate cancer, and decrease in its expression by SPBE would provide a basis for further investigation of its use against BPH and in prostatic cancer chemoprevention. Copyright 2001 Academic Press.