a method is provided for treating human patients who have lymes disease by using a psoralen compound , preferably administered in a dosage of 0 . 3 to 0 . 7 mg / kg , and activating same either in vitro or in vivo using electromagnetic radiation of a prescribed activating wavelength . the activation of the psoralen compound in the presence of a blood fraction from a patient suffering from lymes disease produces a composition which will stimulate an effective immune response to the lymes disease on the part of the patient .