For determining the type of causal agent of infectious diseases and for checking their sensitivity to antibiotics and chemotherapeutic agents in vitro by means of the inhibition zone determination method. Antibiotic assay discs The antibiogram allows rational and selective chemotherapy. The test discs can be coated with chemotherapeutic agents, placed on the innoculated nutrient agar and incubated. The size of the inhibition zone is a measure for the effectiveness of the substances.