Laying hens were fed for a 48-wk period with a basal diet supplemented with a selected strain of Lactobacillus acidophilus at levels up to four million viable cells per gram of feed. Levels of egg production and feed conversion were significantly higher (8 and 14.8%, respectively) than in the control flock, and cholesterol values in yolks were decreased by 18.8%. It is suggested that the latter effect was a reflection of lower serum cholesterol concentrations in treated birds; a maximum reduction of over 55% followed incorporation of the culture into the feed. The level of viable cells in the feed was confirmed as being critical to register the above effects.