In analogy to the immunological method for detecting the presence of cysticercosis in cattle we examined the applicability of the indirect immunofluorescence reaction as a technique for detecting taeniasis in man in 200 sera of tapeworm carriers and 150 sera of controls. Antibodies were found in the serum of most patients (112) infected by Taenia saginata, the test, however, showed widely different titer levels: in 44% of the patients we found false negative and in 1.3% false positive results. Serological investigations on the course of infection were carried out for 21 patients. Differing titer levels and titer variations show the limited applicability of this method in medicine, The importance and desirability of applying immunological techniques for diagnosing Taenia saginala are discussed.