Measurement of volume, pressure, and length were made on eight segments of human cerebral arteries perfused with chymotrypsin (CT) (EC 3.4.21.1) solution (pH = 7.8) for no more than 19 h, and on nine arterial segments perfused with combined enzyme (CT, trypsin (EC 3.4.21.4), elastase (EC 3.4.21.11)) solutions (pH = 7.8) for no more than 4 h. Circumferential tension-strain (and absolute radius) curves were obtained through the Law of Laplace (tension = pressure X radius). Initial and final elastances (tension/strain) were calculated after 0, 0.5, 1.0, 2.0, and 4.0 h of perfusion under the combined enzyme category, and after 0, 0.5, 1.0, 2.0, 4.0, 6.0, and 19.0 h of perfusion with CT. The initial elastance showed a significant increase (0.02 less than p less than 0.05) after about 6 h of perfusion. Increases in the final elastance became significant only after prolonged periods of perfusion with CT. Histological studies using light and scanning electron microscopy confirmed the removal of the elastic lamina as well as portions of the medial region. Fragmentation of the internal elastic lamina did not appear to affect the distensibility of major cerebral arteries in the 50- to 80-year-old age group.