This study has been made at Ege University, Odemis Vocational Training School in 2002 and 2003 on 10-year-old pear trees of the fire blight-susceptible cultivar, Dr. Jules Guyot. Apogee (Prohexadione-calcium; 50 g/acre), Messenger (Harpin Ea protein; 16.5 g/acre), Cropset (a plant-booster element complex; 0.5 I/acre), or streptomycin sulfate (100 ppm; 25 g/acre) were applied to trees in five replicates to determine the efficacy of the antibiotic or systemic acquired resistance compounds for control of fire blight of shoots. Five replicate trees were left as untreated controls. The activators were applied in April when shoots were 10 to 15 cm in length. After treatment, shoots were inoculated with a suspension of Erwinia amylovora containing 10(8) CFU/ml. Two months later, the % of the shoot length blighted (SLB%) was determined by using the formula (a/b) X 100 (a = the length of fire blight lesion and b = total shoot length). In 2002 the SLB% was as follows: streptomycin sulfate = 17.53%, prohexadione-calcium 29.37%, Harpin = 35.04%, plant booster element complex = 60.31%, and control 65.23%. In 2003 the results of the trial were: streptomycin sulfate = 15.80%, prohexadione-calcium = 32.43%, Harpin = 33.39%, plantbooster element complex = 58.52%, and control = 66.97%.