An immunocapture ELISA test for the diagnosis of human and animal influenza A and/or B is described. A monoclonal anti-nucleoprotein (NP) antibody was used to capture the NP antigen and the captured antigen was detected by an anti-NP polyclonal rabbit antiserum. Compared with the usual diagnostic method by cultivation in embryonated eggs, this test had a high specificity (97%) and sensitivity when used for diagnosis using clinical nasopharyngeal samples obtained from patients and animals. Immunocapture ELISA permitted an easier reading than the indirect immunofluorescence technique. It also permitted diagnosis in frozen samples (-20 degrees C) or in infected LLCMK2 cells mixed with uninfected nasopharyngeal cells and kept at 20 degrees C for one week. This test can be carried out in 3 h.