New "reference" circular dichroism spectra of a helix, 0-structure (both parallel and antiparallel), 0-bends, and the unordered form are obtained from circular dichroism spectra and x-ray data for six proteins (myoglobin, lysozyme, lactate dehydrogenase, papain, ribonuclease, and subtilisin BPN'). Circular dichroism spectra for a-helix and antiparallel 0-structure are similar to those for p o l y (~-lysine). The circular dichroism spectrum of the parallel 0-structure is qualitatively similar to that theoretically calculated by Madison and Schellman. The circular dichroism spectrum of @-bends is qualitatively similar to that theoretically calculated by Woody. The spectrum of the unordered form is close to that of the denaturated proteins. These "reference" circular dichroism spectra used for the analysis of the secondary structure of ten globular proteins (besides the six reference proteins D-glyceraldehyde 3-phosphate dehydrogenase, concanavalin A, cytochrome c, and insulin).