The minimum inhibitory concentrations (MICs) of erythromycin against 31 strains of Lactococcits garvicae isolated from diseased rainbow trout were determined. All isolates were sensitive to the antimicrobial agent with MIC values between 0.06 and 0.125 pg ml-'. This study suggests that erythromycin could be used as an effective treatment to control lactococcosis Outbreaks in rainbow trout, although more information on toxicity and efficacy are still needed.