Abstract: Disclosure is made of a plant for continuous cultivation of microorganisms.The plant comprises a closed recirculation circuit made up by a fermenter, a pump and a process parameter measuring unit connected in series by means of an annular duct. The plant also comprises a container for storing a nutrient medium and a finished product collector having a supply line and an overflow connection, respectively. Down-stream of the measuring unit, the annular duct has two locking means; connected to the portion of the duct between the locking means are the supply line and the overflow connection, which accounts for equal volumes of a nutrient medium introduced into the recirculation circuit and of a suspension of microorganisms which is simultaneously discharged therefrom.