The first-order deamidation half-time of the peptide, Gly-Ser-Asn-His-Gly in phosphate butler, pH 7.4, ionic strength at 0.2, 37.0 degrees C, is 6.4 +/- 0.5 days. This compares favorably with the in vivo deamidation half-time of 8 days for this sequence in rabbit muscle aldolase. This fact is discussed with respect to the general hypothesis that sequence-controlled deamidation of glutaminyl and asparaginylresidues is a mechanism by which molecular and organismic development and aging are timed.