The different laboratory technich for the determination of digoxin serum concentrations are analysed. Special emphasis is placed on the radioimmunoassay technic. The advantages and disadvantages of this technic are studied and the standard curves obtained in our determinations (n=39) are analysed. It can be seen that they can be reproduced in all cases with a high degree of similarity. The possible causes of error in this microtechnic are also analysed and a modification in the decanting fase, with which the number of repetitions in our laboratory has decreased, is suggested. Finally the criteria for the actual evaluation of the seric digoxin levels used in our laboratory are described and new possibilities in pharmacological investigation by this technic are mentioned.