With the aim of finding laser glasses operating in CW at room temperature, a comparative study was made of various neodymium-doped vitreous substances: silicate, borate, germanate, phosphate, and fluoride glasses. About 500 samples of phosphate glasses, doped with neodymium, were prepared and their optical properties studied. The phosphate glasses have three main advantages for laser action. 1) The fluorescence band is narrower than in silicate glasses and can be as sharp as 153 Å. 2) The optical pumping is more efficient in phosphate glasses. 3) The lifetime of the 4F3/2level is about 300 μs. The phosphate glasses have very interesting laser characteristics, i.e., in pulsed operation the threshold is 1 joule. Such a rod exhibits semicontinuous operation at room temperature pumped by a krypton arc lamp; when excited in ac, the threshold is about 1 kW. It was found that the fluoride glasses have even more promising laser properties.