To further understand the occurrence of N-glycosylation, 21 nonhomologous proteins with Asn-x-Ser/Thr sequence were investigated. The results showed that some oligopeptides with Gly residues (G-x-y or y-x-G) are adjacent to the N-glycosylated sequences. These oligopeptides are not only essential for the structure and function of the proteins, but they are also found to be often proteolytic processing sites. These properties suggest that these oligopeptides may be a "sequence pattern" for the occurrence of N-glycosylation. The implications of the findings for protein structure and function are discussed.