Abstract: In this paper, the calculation method of total drug and plasma drug concentration after iv and oral administration of a drug at inconstant dosage intervals of onecompartment multiple-dose pharmacokinetic model were discussed. Two formulae: the recursion formula and the general formula obtained by mathematical induction were given. Formulae of calculation of peak time, peak height and plasma drug concentrations at steady state were also reported. In addition, the program was carried out on the digital computer (DJS-131).