The effect of growth-stimulating agents (15 ppm of virginiamycin, 10 ppm of avoparcin and 12 ppm of nitrovin) and that of seven days' treatment with 300 ppm of furazolidone on the performance of broilers was studied in an experimental study of 9,600 animals. Furazolidone was fed in either the fourth or the fifth week of life and combined with virginiamycin or nitrovin. Non-significant improvements in growth were observed when virginiamycin (1.5 per cent), avoparcin (0.7 per cent) and nitrovin (0.7 per cent) were administered. Treatment with furazolidone for seven days resulted in substantial retardation of growth. When broilers were treated during the fourth week of life, the retardation of growth was largely compensated for during the other two weeks. Treatment in the fifth week of life resulted in lower weights prior to slaughter. Therefore, care should be taken in recommending treatment with furazolidone at the end of the fattening period of broilers.