Orchard experiments in southwestern Ontario Canada showed that both oxytetracycline hydrochloride (OTC) and streptomycin sulfate significantly (P .ltoreq. 0.01) reduced defoliation and/or leaf infection due to bacterial spot (Xanthomonas pruni (E.F.Sm.) Dows.) in peach (Prunus persica (L.) Batsch). Fruit infection was also similarly reduced by OTC but data for streptomycin was limited by the low incidence of bacterial spot in the dry summer of 1976. Schedules of 8 OTC or streptomycin sprays or 4 OTC sprays were as effective as extended schedules of 12 sprays. Both OTC and streptomycin sprays reduced leaf surface populations of X. pruni. There was no detectable residue of OTC in peaches sampled 20-30 days after the last spray. In monitoring trials in 1977, OTC-resistant isolates of X. pruni were not found.