For successful rearing of purchased calves, healthy animals with good utiization of feed are main objectives for profitability. Growth rate feed conversion efficiency (FCE) and health are adversely affected by pathogenic bacteria and antibiotics or chemotheraputic agents have been used as feed additives for several years. These may depress useful, non pathogenic bacteria and certain strains of pathogenic bacteria may become resistant to antibiotics. Probiotics are becoming increasingly advocated as being of benefit to calf rearers as a feed additive to improve the growth rates and health of rearing calves. An experiment at Drayton E.H.F. investigated the use of Lactobacillus acidophilus as a probiotic agent during the rearing period of purchased calves.