The treatment of diseases or secondary infections due to the following bacteria sensitive to ampicillin in dogs, cats, cattle, pigs and sheep and where prolongation of activity from a single injection is required: Streptococcus spp., Actinomyces pyogenes, Mannheimia haemolytica, Pasteurella multocida, Erysipelothrix rhusiopathiae, Staphylococcus aureus and Staphylococcus spp.