Media for the selective cultivation of bacteria of the Corynebacterium species, others being inhibited by the inclusion of potassium tellurite, usually at a strength of 0.035 -0.04 per cent. In McCleod’s medium a heated rabbit-blood agar is employed; in Hoyle’s medium the agar includes laked blood; Monckton’s Enrichment Medium is a digest broth including the potassium tellurite with copper sulphate and laked blood, the incubated broth culture being sub-cultured to solid media. Corynebacteria colonies are grey or black on tellurite media, and their morphology may aid species identification, which is confirmed by fermentation tests in dextrose, sucrose and starch, urease activity, and haemolysis on blood agar.