It is well known that in healthy individuals as well as in patients with diseases receiving glucocorticoids in a given dosage, there is a wide variation in blood concentrations. These may be of importance not only for the efficacy of treatment, but also for the occurrence of side effects. Pharmacokinetic information on glucocorticoids, is scarce mainly because of lack of suitable methods of analysing these drugs in body fluids. A high pressure liquid chromatography (HPLC) method has previously been used for determination of methylprednisolone in plasma (Garg et al., 1977). After modification, this method has been used for determination of methylprednisolone in plasma in healthy subjects and patients with renal transplants. Preliminary data are presented showing a good reproducibility of the method.