Abstract: The method of calculating potency and its confidence limits in bioassay was studied. A set of general formulas was worked out by mathematical inference and demonstrated with example. The results showed that thegeneral formulas are applicable to the calculation of potency and its confidence limits in parallel line assays of various dose designs including those listed in the Chinese Pharmacopoeia (1995) and many other special dose designs. The calculation procedures can be remarkably simplified and easily programmed by using the formulas. Nevertheless, the computation results are identical with that obtained from standard procedures.