The clinical course, post mortem lesions as well as virological and serological results after simultaneous intranasal inoculation of pigs with bovine viral diarrhoea virus (BVDV) and hog cholera virus (HCV) are described. Five groups of four weaners received constant doses of BVDV strain OSLOSS/2482 and tenfold decreasing doses of HCV strain ALFORT/187. Doses of 1,000 and 100 TCID50 of HCV in groups A and B of pigs led to fever and severe clinical signs in all animals of two groups, whereas at higher dilution of inoculum two, three or four animals survived without any clinical signs in the respective groups (C-E). Leucocyte samples taken from febrile animals and from normal pigs on five consecutive days were inoculated into both fetal calf kidney (FCK) and PK (15) cell cultures. Virus isolates were differentiated with BVDV and HCV specific monoclonal antibodies. HCV viraemia was detected in febrile animals exclusively, and BVDV viraemia occurred in not affected animals on days 3 to 7 post inoculation. Neutralizing antibodies (nab) against BVDV appeared before HCV nab in surviving animals of groups C and D after receiving low doses of HCV (10 or 1 TCID50). No BVDV nab were detected in group E that had received such a high dilution of HCV in addition to BVDV that theoretically no HCV was applied.