AbstractThree simple linear and three simple non‐linear pharmacokinetic models are presented which incorporate the reversible metabolism that occurs between prednisone and prednisolone. Under steady‐state conditions it is possible to not only distinguish between the linear and non‐linear models but also to determine which particular model of each group applies to a given set of data. While the non‐linear conversion of prednisolone to prednisone is important in explaining the pharmacokinetics of prednisone in all three non‐linear models, the same is not true for pre