This case report describes the successful treatment of a three-month-old lame foal. Radiographs confirmed a septic physitis of the right distal tibia, which was unresponsive to initial antibiotic therapy. Culture of the lesion grew Rhodococcus equi. Systemic antimicrobial therapy was changed to rifampin and clarithromycin, and intravenous regional limb perfusions with erythromycin were performed daily for four days. Within 24 hours the lameness was improved. Swelling around the lesion was reduced, and previously abnormal clinical parameters were returned to within normal limits. The filly continued to recover and was turned out without complications one-month post-discharge. This case discusses the use of erythromycin IVRP as a treatment for septic physitis caused by Rhodococcus equi.