The aim of this paper is to research the role of probiotics in calf diets on the example of the court case. Probiotics are specially treated and adjusted microorganisms or their vegetative forms which, when given in the right quantity, improve the host’s health. They improve the growth intensity, reduce the cost of feed per unit gain, improve the immune system, protect from infectious diseases and lower the mortality rate. The importance of the probiotics usage in calf diets is in their role in producing and maintaining the intestinal flora. The usage of probiotics decreased the frequency and shortened the duration of diarrhoea, which is considered to be one of the leading causes of illness and death in calves. The interest in the usage of probiotics as the animal feed supplement has increased during the last few years because of the increased number of banned antibiotic growth promoters. Most researches carried out on calves show the efficacy of adding different probiotics to fodder. On the other hand, some researches have shown that probiotics have small or no influence on calf diets. This paper shows a legal case in which the plaintiff demands compensation for the dead calves and claims that the cause of their death was the diet – a milk substitute which contained a probiotic. This substitute had been produced by the defendant. Bacterium Bacillus cereus had been used as the probiotic. The Croatian Veterinary Institute has bacteriologically tested the sample of the milk substitute and isolated a toxic bacterium Bacillus cereus and not a probiotic Bacillus cereus var. toyoi. The failure in the process of production (the use of insufficiently treated bacteria strains – probiotics), inadequate storage and producing animal feed which contains a probiotic can cause health problems and death of calves.