The antitumor activity of calicheamicin is related to its ability to bind to and cleave double-stranded DNA. There is substantial evidence that the oligosaccharide-aryl tail of calicheamicin plays a critical role in the binding selectivity. The calicheamicin oligosaccharide contains some unusual structural elements that may be related to the DNA binding function. A better understanding of how structure is related to function in the calicheamicin oligosaccharide could result in an ability to design new DNA binders. In this paper, the influence of the hydroxylamine glycosidic linkage on the shape of the calicheamicin oligosaccharide is analyzed in detail using a combination of experimental data and molecular mechanics calculations. As part of this work, parameters for N-O bonds have been developed for use with the program DISCOVER (AMBER force field). The analysis indicates that the unusual N-O bond in calicheamicin, with its distinctive torsion angle preferences, organizes the two halves of the molecule into a shape that complements the shape Of the minor groove.