The described system and method for blood treatment are configured to detect at least two hemodynamic parameters, for example the blood pressure and the relative blood volume, during the blood treatment. At least two fuzzy modules receive measuring values of the hemodynamic parameters as input variables, wherein the output signals transmitted by the fuzzy modules are weighted by at least one weighting module. A setting means effectuates setting of at least one variable, for example an ultrafiltration rate, a dialysis fluid conductivity or a dialysis fluid temperature, in response to the output signal transmitted by the weighting module. In this way, e.g. threatening intradialytic hypotensive episodes can be detected and avoided. The system can be designed as a dialyzer for hemodialysis, hemofiltration or hemodiafiltration.