The present invention relates to a method of flushing a dialyzer with a flushing liquid, wherein the dialyzer is arranged in a dialyzate-side circuit of a blood treatment device and wherein the dialyzer has at least one dialyzate-side chamber which has at least one inlet and at least one outlet for the flushing liquid and which is flowed through by the flushing liquid, wherein at least one property of the flushing liquid is measured at the outlet of the dialyzer or downstream of the dialyzer in the dialyzate-side circuit to obtain one or more outlet-side measured values, wherein the property depends on the quantity of the air in the flushing liquid.
