the invention provides an improved method for potentiating the antineoplastic activity of 5 - fluorouracil with levamisole , or with an analogue thereof . specifically , the invention provides regimens wherein levamisole is administered contemporaneously with the administration of 5 - fluorouracil , thereby increasing the exposure of tumor tissue to the simultaneous presence of the two drugs . the invention further provides methods for the parenteral administration of levamisole , thereby overcoming the disadvantages associated with inter - patient variability in the bioavailability of oral .