Colonies of Arcanobacterium haemolyticum on common blood agar can be easily overlooked. Therefore a diagnostic medium was developed, on which A. haemolyticum colonies produce a con- spicuous zone of complete hemolysis. The medium under question is blood agar prepared from the Columbia Blood Agar Base and 5% washed sheep erythrocytes sensitised with equi factor (EF) of Rhodococcus equi. Optimally, 10 activity units (AU) of EF per 1 ml were used. EF was titrated on a non-nutrient medium consisting of agar Purified (Difco) and 5% washed sheep erythrocytes sensitized with b-haemolysin (BL) of Staphylococcus aureus, 10 AU/ml. On the same medium, staphylococcal BL was titrated on the basis of its direct haemolytic effect. Despite the very distinct haemolytic reaction of the control strains evident on the diagnostic medium with EF, A. haemolyti- cum failed to grow from 2.597 throat swabs examined especially for the particular microbe during the a period of two years. However, A. haemolyticum was isolated on this medium twice from 223 swabs from wounds and skin lesions. The proposed medium makes also the rapid diagnosis of species Corynebacterium ulcerans, Dermatophilus congolensis and Listeria monocytogenes on the basis of haemolytic synergism possible.

        Key words: Arcanobacterium haemolyticum – diagnostic medium – haemolytic synergism – equi