The use of the penicillins in veterinary dermatology is discussed. An outline is provided of the main penicillins used in the veterinary ®eld. These include benzyl penicillin, penicillin V, ampicillin, amoxycillin, coamoxiclav and oxacillin. An increase in b-lactamase production among strains of Staphylococcus intermedius, the principal canine pathogen in pyoderma, has been seen in recent years. Thus only those penicillins with resistance to b-lactamase (co-amoxiclav or isoxazolyl penicillins) are likely to be of value in treating canine pyoderma. However, feline, porcine and equine staphylococcal dermatoses, and other veterinary dermatoses such as the actinomycoses, dermatophilosis and erysipelothrix, usually respond well to most penicillins, whether or not they resist b-lactamase.