Saccharomyces boulardii is a yeast employed in the treatment of diarrhea. We present here the results of a study measuring the relative activity of this yeast in four different formulations available in Chile. The activity was assessed by determining both the number of live cells after re-hydrating the products and the growth observed in the product suspended in culture medium. In each experience the product Perenteryl® showed a faster growth, reaching maximum cell density values three to five hours earlier that the other products. Though the total number of cells was practically the same in each product, the number of live cells was larger in the product Perenteryl®