Benign prostatic hyperplasia (BPH) is the benign uncontrolled growth of the prostate gland, leading to difficulty with urination. Saw palmetto lipid extracts (SPLE), used to treat BPH, have been shown to inhibit prostate 5a-reductase, and some major components, such as lauric, myristic and oleic acids also inhibit this enzyme. Coconut oil (CO) is also rich in fatty acids, mainly lauric and myristic acids. We investigated whether CO prevents testosterone-induced prostate hyperplasia (PH) in Sprague-Dawley rats. Animals were distributed into seven groups (10 rats each). A negative control group were injected with soya oil; six groups were injected with testosterone (3 mg kg(-1)) to induce PH: a positive control group, and five groups treated orally with SPLE (400 mg kg(-1)), CO or sunflower oil (SO) (400 and 800 mg kg(-1)). Treatments were given for 14 days. Rats were weighed before treatment and weekly thereafter. Rats were then killed and the prostates were removed and weighed. CO (400 and 800 mg kg(-1)), SPLE (400 mg kg(-1)) and SO at 800 mg kg(-1), but not at 400 mg kg(-1), significantly reduced the increase in prostate weight (PW) and PW:body weight (BW) ratio induced by testosterone (% inhibition 61.5%, 82.0%, 43.8% and 28.2%, respectively). Since CO and SPLE, but not SO, contain appreciable concentrations of lauric and myristic acids, these results could be attributed to this fact. In conclusion, this study shows that CO reduced the increase of both PW and PW:BW ratio, markers of testosterone-induced PH in rats.