In this paper it is presented a detailed fiber analysis of leaves of twenty mature sisal plants taken from four positions on the plant: 1) first developped leaves (75°); 2) leaves usually cut for fiber extraction (50°) ; 3) leaves adjacent to the central bud (25°) ; and 4) young leaves not yet unfolded from the central bud (0°). The results herein reported are against the prevailing opinion that the sisal leaf only matures after it has unfolded from the central bud. Neither the physical nor the chemical fiber characteristics were adversely affected even if cutting was carried out up to the very young leaves. This practice, however, cannot yet be advised, as it desirability also depends on the effects of the severe cutting upon the subsequent rate of growth of the new leaves. A cutting trial including the cut of all leaves every four months is still in progress. Preliminary results have shown that the plants of this treatment were able to develop eight leaves until the second cut, with an average fiber content of 3,7%.