This study presents the first nucleotide sequence and deduced primary amino acid sequence of a subtype H1 haemagglutinin from the avian influenza virus A/duck/Alberta/35/76 (H1N1). The molecule is structurally, antigenically and molecularly similar to H1 haemagglutinins of human viruses but sequence homology differences indicate that there has not been a recent transfer of haemagglutinin genetic information between them.