Thirty calves naturally infected with Moraxella bovis were divided into two equaL groups. One group was injected with fLorfenicoL, the other group with Long-acting oxytetracycline. The animals in each group were examined over 10 weeks to compare differences in the progress of eye Lesions and in their respective healing periods. Animals treated with fLorfenicoL recovered more rapidly than the animals treated with oxytetracycline. In contrast to the animals in the fLorfenicoL group, eye Lesions reoccurred in some animals six weeks after the injections of oxytetracycLine. Antibiotic sensitivity of M. bovis isolated from the conjunctival sacs of infected animals was determined and fLorfenicoL was found to be the most effective antibiotic tested. Thus, florfenicol was found to be a more effective antibiotic against M. bovis in vivo and in vitro than Long-acting oxytetracycline.