During the hunting season from 1991/1992 blood samples were collected from wild boar shot in the Federal States of Sachsen-Anhalt (482 samples) and Brandenburg (177 samples) which corresponds to 2.1 and 0.4% of the total hunting bag. All sera were screened in a complex trapping blocking (CTB) ELISA for antibodies against hog cholera virus (HCV) and in an indirect ELISA for antibodies against Aujeszky's disease virus (ADV). Additionally the sera were tested for neutralizing antibodies against HCV strain ALFORT/187, bovine viral diarrhoea virus (BVDV) strains NADL and 1138/69, and against an ADV field isolate. In case of questionable results sera were tested against HCV strain "BERGEN", HCV vaccine strain "RIEMS" and three HCV field isolates from wild boar. The serological testing for antibodies against "porcine reproductive and respiratory syndrome virus" (PRRSV) was carried out in indirect immunoperoxidase monolayer assay (IPMA). Four sera (Sachsen-Anhalt) reacted positive in CTB-ELISA. Seven sera yielded neutralizing antibodies against HCV but only one of the "non-negative" samples scored positive in both techniques, ELISA and VNT. Two sera (Brandenburg) had low neutralizing antibody titres against Alfort/197 but scored negative in CTB-ELISA. Screening for antibodies against ADV of 640 sera led to 13 positive sera including 5 positive findings in both ELISA and VNT. Antibodies against PRRSV were detected in two sera which were collected Sachsen-Anhalt. Estimations resulted in a prevalence of about 5% for antibodies against HCV.