The indirect hemagglutination-test (IHA) and the indirect immunefluorescence-test are two modern methods for the serological diagnosis of an echinococcosis. If both tests are employed, the disease can be diagnosed with great reliability. A titer of 1 : 128 in the IHA makes the diagnosis of an echinococcosis very likely; a titer exceeding 1 : 1000 is significant. Serological tests of 36 patients with E. cysticus and E. alveolaris are evaluated; the interpretation of the results is discussed. In all patients the diagnosis was established between October 1977 and October 1978. In Germany the complement fixation test is commonly used to diagnose an echinococcosis. This test, however, is unreliable and fails in one third of all cases. It should be--as well as the Casoni skin-test--replaced by more sensitive and specific reactions. If the complement fixation test is positive, it might be used for postoperative controls. Compared to previous years the disease-rate among Germans is rising. The main reason seems to be the increasing tourism to foreign countries. Serological tests in small laboratories are unreliable and make an evaluation difficult. The diagnosis should be established in specialized centres.