The sequence of the genes encoding the fusion (F) and hemagglutinin-neuraminidase (HN) glycoproteins of the human parainfluenza 3 virus was determined by molecular cloning. The genes were cloned by primer extension using genomic 50 S RNA as the template. A series of four overlapping clones was generated from the 3' end of the fusion gene which extended across the gene end and intergenic boundaries of the F-HN and HN-L genes. The F gene extends 1851 nucleotides (inclusive of the putative transcription initiation and polyadenylation signals) and encodes a protein consisting of 539 amino acids (mol wt 60,067). This protein contains four potential sites for N-linked glycosylation in the F1 subunit polypeptide and none in the F2 subunit polypeptide. The lack of a potential site of glycosylation in F2 makes this protein unique compared to other reported paramyxoviral F proteins. The HN gene extends 1888 nucleotides and encodes a protein consisting of 572 amino acids (mol wt 64,255). This protein contains four potential sites for N-linked glycosylation.