Potato – agar medium for the cultivation of Bord. pertussis, not incorporating peptones, some of the constituents of which are inimical to the growth of this species. To the base potato – glycerol – agar are added, when pouring, cysteine – magnesium salt mixture, 4:4-diamidodiphenylamine dihydrochloride solution, penicillin and finally over half the agar volume of fresh defibrinated horse blood. Acinetobacter parapertussis is inhibited by this medium.