The probiotics that need refrigeration are those that contain probiotic bacteria still in the growth phase. They are replicating and consuming nutrients. With refrigeration, the metabolism of the bacteria slows down, and they continue to consume nutrients but do so more slowly. Refrigerated probiotics can be left at room temperature for a few days and sometimes even several weeks without losing a great number of viable organisms. However, you still want to follow the label and refrigerate them as instructed.