The effects of deacylating the H3 influenza hemagglutinin (HA) on its membrane fusion activity were investigated. Chemical deacylation caused no change in the ability of HA to fuse liposomes in vitro. Site-specific mutagenesis of the three cysteine residues in the cytoplasmic tail singly, or in combination, showed that all three were palmitoylated. Substitution of one, two, or all three cysteines with serine and subsequent lack of palmitoylation at mutated sites had no effect on the pH of the conformational change in HA required for fusion activity or the extent of fusion activity.