Abstract: Disclosed herein are four embodiments of a system specifically applicable to the hemodialysis procedure. Two embodiments, configured as single pass and recirculating dialysate systems, control ultrafiltration rate to a preset value and measure ultrafiltration rate and the total quantity of ultrafiltrate removed. These embodiments are useful when the filtration characteristics of the dialyzer, i.e., semipermeable membrane, are constant and known. However, when the filtration characteristics of the dialyzer, i.e., semipermeable membrane, are not constant and known, two other embodiments, configured as single pass and recirculating dialysate systems, control transmembrane pressure to a preset value and measure ultrafiltration rate and total quantity of ultrafiltrate removed. All embodiments are closed systems requiring sealed dialyzers. Each of the foregoing systems include, inter alia, a unique flow measurement pressure control unit which controls fluid pressure and simultaneously meters fluid flow therein.