A semi-field study was carried out to evaluate the effect of two medicinal herbs, individually and in combi-nation, on growth performance, carcass traits, nutrient digestibility and immune response of broiler chick-ens. A total of 384 one-day-old straight-run Arbor Acres broiler chickens were allocated into 24 floor pens prepared in a commercial broiler house. Pen-groups were fed one of the following five diets for 42 days: a basal corn-soybean meal diet as control (5 pens), the same basal diet plus 200 ppm virginiamycin (V; 4 pens), the same basal diet supplemented with 0.4% peppermint (Mentha piperita) leaves (P; 5 pens), 0.4% tarragon (Artemisia dracunculus) leaves (T; 5 pens) or with 0.2% tarragon leaves + 0.2% peppermint leaves (P+T; 5 pens). The results showed that performance traits, including average body weight, body weight gain, feed intake and feed conversion ratio were not affected by dietary treatments (P>0.05). No significant differences were detected between the control and experimental groups in apparent digestibility of nutrients and antibody titer against newcastle disease virus (NDV). Slaughter traits of herb or antibiotic supple-mented groups did not differ significantly from those of the non supplemented control group. In conclusion, the additives tested had no impact on broiler growth and health status.

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