Objective To investigate changes in glycosaminoglycan (GAG) profiles in human prostatic tissue. Materials and methods Seventeen human prostatic samples were examined; five were normal, six hyperplastic and six were cancerous. Prostatic proteoglycans were extracted with 4 mol/L guanidine‐HCl containing protease inhibitors. After digestion of the freeze‐dried proteoglycan extract with papain, the prostatic GAGs were purified. Total GAGs were measured by a modified dimethylmethylene blue (DMB) method. High‐performance liquid chromatography (HPLC) was used to quantify the extracted GAGs. Results Six types of GAGs, i.e. chondroitin 4‐sulphate (Ch‐4S), chondroitin 6‐sulphate (Ch‐6S), dermatan sulphate (DS), chondroitin, heparan sulphate and hyaluronic acid, were analysed qualitatively and quantitatively. The total amount of GAGs was increased in hyperplastic and cancerous prostates, with the predominant components being DS and Ch‐6S in these specimens. The Ch‐S:DS ratio in cancerous prostate was significantly higher than that in normal and BPH tissue (PP<0.01). Conclusions These results suggest that an increase in chondroitin levels may be associated with hyperplastic change and an increase in the Ch‐S:DS ratio may be related to the development of malignancy.