The effects of yogurt and acidophilus yogurt on the weight gain, serum cholesterol, high density lipoprotein cholesterol, low density lipoprotein cholesterol, triglycerides, and the numbers of fecal lactobacilli and coliforms were investigated in mice assigned to three dietary treatments for 56 d: 1) commercial rodent chow and water (control), 2) commercial rodent chow and yogurt made from milk inoculated with a 3% (vol/vol) liquid culture of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus (yogurt), and 3) commercial rodent chow plus yogurt made from milk inoculated with a 0.01% (wt/vol) freeze-dried culture of Streptococcus thermophilus plus Lactobacillus acidophilus. The weight gains of mice receiving yogurt or acidophilus yogurt were higher than those of the mice in the control group. The mean values for serum cholesterol concentrations and LDL cholesterol concentrations were significantly decreased when acidophilus yogurt was fed on d 28 and 56. High density lipoprotein cholesterol and triglycerides were not affected by yogurt or acidophilus yogurt. The highest number of fecal lactobacilli was found in mice receiving acidophilus yogurt, and the number of fecal coliforms of that group was also lower than in the other two groups.