Primary lesions are directly associated with the disease process and they are not necessarily pathognomonic, but give a valuable clue as to the type of disease process occurring. Pustules and vesicles rapidly rupture in dogs and cats to form crusts. This chapter shows papules, pustules and epidermal collarettes on the ventral abdomen of a dog with a staphylococcal pyoderma. Secondary lesions are a result of trauma, time and degree of insult to the skin and these are much less specific than primary lesions. Impression cytology is performed to look for organisms such as yeast or bacteria on the surface of the skin. Tape cytology is useful to sample dry or scaly areas, or areas where a slide cannot be pressed and it is highly effective unless the skin is moist, when the tape will not stick. Remember that skin disease does not occur in isolation – always do a thorough general examination to detect any systemic complications or concurrent conditions.