We have examined the consequences of cleaving the fusion glycoprotein (F) of human respiratory syncytial virus (HRSV) at two distinct furin-recognition sites. Purified anchorless F is a mixture of unaggregated cone-shaped molecules and rosettes of lollipop-shaped spikes. The unaggregated molecules contain a proportion of uncleaved F0 and an intermediate, FΔ1–109, cleaved only at site I, residues 106–109. Inhibition of cleavage at site I, by two amino acid changes (R108N/R109N), reduces the proportion of aggregated molecules with a concomitant increase in the amount of unprocessed F0. Inhibition of cleavage at site II, residues 131–136, by deletion of four amino acids (Δ131–134), abrogates aggregation of anchorless F and all molecules are seen as individual cone-shaped rods. In vitro cleavage of anchorless F, or mutant Δ131–134, with trypsin at 4, 20, or 37°C, under conditions in which cleavage at site II is complete in all molecules, leads to their aggregation in rosettes of lollipop-shaped spikes. Thus, cleavage at site II is required for the structural changes in anchorless F that lead to changes in shape and to aggregation. The segment between sites I and II, residues 110–136, is not associated with anchorless F in the supernatant of infected cell cultures, indicating that it is released from the processed protein when cleavage at sites I and II is completed.