Methods of combined sterilization and integrity testing of dialyzers such as hollow fiber dialyzers are disclosed. Sterilization and integrity testing may be performed by treating the dialyzer with a sterilization fluid for sterilizing at least the blood-side compartment of the dialyzer and for wetting the dialysis membrane of the dialyzer with the sterilization fluid, and carrying out an integrity testing of the dialysis membrane wetted with the sterilization fluid, wherein the sterilization fluid is selected from aqueous solutions containing peroxide and/or ozone, the peroxide being selected from peroxides which disintegrate into water, oxygen and/or volatile organic compounds, and from aqueous solutions containing chlorine, bromine and/or iodine.