Rats' bladders were irrigated with aqueous solutions of chlorhexidine digluconate 1 : 5,000 or 1 : 10,000 for varying periods up to 48 hours. Histologic examination of the bladders showed severe erosive cystitis in a high percentage of cases. It is concluded that chlorhexidine cannot be recommended for prolonged irrigation of the bladder or for instillation during the intermittent catheterisation where chlorhexidine has repeated and prolonged contact with bladder mucosa.