Abstract A one-week sample of eggs was collected from 10 individually housed brown-egg laying hens at 43 weeks of age and again at 75 weeks of age. One egg from each hen at each age with a specific gravity nearest the mean for that hen was chosen for further analyses. Eggs laid by the younger hens had a significantly higher specific gravity than those laid by the older hens. Amino acid analysis was performed on the outer portion of the outer shell membrane. The weight percentage of amino acids in the dried membrane was significantly less for the 75-week-old hens. There was no significant correlation between egg weight and weight percentage of amino acids. Analysis of covariance using a stepwise regression procedure indicated that the changes in specific gravity are due to a combination of age and amino acids and not to age alone. Age alone did not account for a significant part of the variability in the observed specific gravity. Three amino acids — aspartic acid, proline, and phenylalanine — in conjunction with age accounted for over 80% of the variability observed in specific gravity. These studies further implicate the shell membrane as a determinant of shell quality.