This paper deals with the variation of fiber dimentions in growth rings taken at the breast height (B.H.) and at three aditional level of trunk height (10%, 20% and 30% of total height) of two plants of Eucalyptus saligna Smith. Statistical analyses of variance for fiber length, fiber diameter and fiber thikness in diferent growth rings at B.H., 10%, 20% and 30% of trunk height is prsented. Analysis of variance allowed the following conclusion: 1° - Significant diferences were observed for fiber dimentions mean, taken at B.H. and those taken at the levels of 10%, 20% and 30% of trink height; 2° - In any growth rings along the trunk, the fiber length means increased consistently from B.H. to the levels of 10%, 20% and 30% of trink height, however the means for fiber diameter and thikness of the wall decreace from the B.H. point to the leves of 10%, 20% and 30% of trink height; 3° - The results obtained in the present study confirm those obtained by BISSET & DASDWELL (1949) in that the maximum fiber lenght is reached at aproxmately one third of the total height of the trink and also confirm the afirmation made by RUDMAN et al (1969) that the samples taken at the B.H. level are inadequate for qualitative wood studies, specially in raltion with forest genetics investigation.