Concrete columns have been the subject of research for many years. However, little is known about the behavior of slender columns and, in particular, of slender prestressed concrete columns. The increased use of such columns has encouraged research, both theoretical and experimental, in order to determine the effects of many variables on their behavior and strength. Some aspects of such an investigation(') are described in this paper. Theoretical failure loads are presented, obtained from the analysis of some 300 columns. These were slender, axially pretensioned, eccentrically loaded columns, with equal end eccentricities, and with a possible initial deflected shape (Fig. 1). The variables considered were prestress, eccentricity, slenderness, concrete compressive strength, concrete tensile strength, initial curvature, and area of steel. The details of the cross-section used in the analysis, are shown in Fig. 1. They also represent the typical dimensions of 36 columns, tested to substantiate the theory. The good agreement obtained between experimental and theoretical results(') provides confidence in the theoretical analysis considering additional variables. The variables investigated experimentally !were eccentricity (e/d = 1/8, 3/4 and 2), slenderness (Lid = 20, 30 and 40), and prestress (f ,y/ f ' = 0.1, 0.3 and 0.5). Since the prestress losses were somewhat underestimated, the above prestress ratios are nominal values. The average values of the actual prestress ratios were 0.09, 0.25 and 0.41, and these were used in the theoretical analysis. The theoretical analysis is based on a finite element approach and uses iteration and suitable numerical methods. A computer program was written which gave, for each particular column, the buckling load based on the cotangency criterion, and the full load-deflection and Ioadstrain curves. The mode of failure, i.e. instability or material failure, was also indicated. The deflected