During a 95-day study period in 1995 in Denmark, 18 ostriches in a flock of 77 ostriches and four emus held in quarantine died. Clinical and pathological observations did not indicate the presence of transmissible infectious disease in the flock. Management failures and indoor housing were believed to have contributed significantly to the number of deaths. Samples from 17 of the dead ostriches were examined virologically. Three isolates of avian paramyxovirus serotype 1 (APMV-1) were obtained from intestines and intestinal contents of dead ostriches submitted for laboratory investigations. In ICPI tests in day-old chicks values for the three APMV-1 isolates were in the range 1.63-1.69. Characterization by means of mouse monoclonal antibodies and by restriction site analysis revealed that the three isolates were indistinguishable and similar to APMV-1 viruses present in a simultaneous epizootic of Newcastle disease in back yard poultry in Denmark. Blood samples were taken from all live birds in the flock after 25 and 95 days of quarantine and all were negative for antibodies to APMV-1 in haemagglutination inhibition tests. All samples taken after 95 days of quarantine were also negative for antibodies to APMV-1 in serum neutralization tests performed in chicken embryo cells. Blood samples taken after 95 days of quarantine were tested in a commercial ELISA for antibodies to APMV-1. In this test 35% of the samples were positive, 35% were border line and 30% were negative.