Deep cutaneous bacterial infections pose an often frustrating diagnostic and therapeutic challenge for the veterinarian. Diagnostic key aspects, that should be based on a systematic and orderly protocol, will be presented, and we will focus on 3 fundamental aspects: -Identification of the typical injuries of a deep pyoderma. -Confirmation of the presence of bacteria by cytological examination and the performance of a culture / sensitivity test to know their resistance profile. -Investigation of predisposing factors and / or primary / underlying diseases associated with deep pyoderma.