We are developing a new spectrophotometric temperature index based on the Ca II H and K lines. Because these lines are present even in very cool stars and because the Ca II H line is blended with the H-epsilon line in hot stars, this index should cover a very broad range of spectral types. Our data set consisted of 95 stars with spectral types ranging from O9 to M1. We examined five different indices based on the Ca II H + H-epsilon and K lines, as well as single-wavelength indices centered on each of the H-delta and H-gamma lines, which are in the same region of the spectrum. We compared our new index value with the H-beta index values for the stars in our data set that had published H-beta values. We found that the Ca II K-H index was the best temperature indicator with the widest range in magnitude of the indices we examined.