The length of elastic fibers and the distribution of fiber diameters was determined by morphometry in the parenchyma of human lungs. Studies were done on 33 lungs from male subjects 1 to 85 years of age, including 9 lungs with mild emphysema. These studies suggest that the total length of elastic fibers is present early in life, possible by 10 years of age, and thereafter remains constant. Average fiber diameter increases between infancy and adulthood but probably does not change further beyond the third decade of life. No significant differences could be detected in either total fiber length or fiber diameter in the lungs with mild emphysema compared to normal lungs of the same age.