We have developed a double antibody sandwich (antigen capture) ELISA for the detection of Derzsy's disease virus (GPV-1) antigen produced in cell cultures. This provided unambiguous quantification of virus whereas evaluation of cytopathic effect was sometimes difficult. A blocking ELISA was developed to quantify anti-GPV-1 antibodies in goose sera. This method was rapid, simple, easily standardized and correlated well with a virus neutralization test.