Low-dispersion near-infrared slit spectra of a sample of M, S, and carbon stars have been examined. It has been found that the spectral types of twenty-nine I-type long-period variables observed near minimum light define a period-spectrum relation which parallels, at about three subtypes later, the analogous relation for types at maximum light. Changes in molecular-band strengths as a function of phase in the spectra of several stars reaffirm the temperature changes in M and S long-period variables. Four unidentified infrared bands probably characterize the cooler S stars with high Zr/Ti abundance ratios. Infrared spectra of R Cygni indicate that the four bands are quite sensitive to phase in the light cycle. A small sample of carbon stars has been classified according to criteria in the visual spectral region. Evidence is presented that the infrared bands of the red cyanogen system weaken at spectral types later than C7. In addition, infrared spectrograms of three stars intermediate between carbon and S exhibit cyanogen-band strengths comparable to those found in the latest and presumably coolest carbon stars. It is suggested that the nitrogen abundance in the atmospheres of stars with S characteristics is high relative to carbon stars and that a possible source of the ultraviolet opacity in N and carbonS stars is the CN molecule.