This paper presents results from a number of studies where different BCG products and BCG strains were compared and evaluated by the immediate effect after vaccination. It was shown that BCG strains differ in terms of allergenic potency. However, two products prepared from the same strain in different laboratories may differ more than two products prepared from different strains in one laboratory. Thus for products prepared from different strains in different laboratories the allergenic potency may differ as a result of differences between strains, production methods and concentrations. Any difference in allergenic potency observed between products from different laboratories, therefore, cannot give conclusive information on a single characteristic.