The scintillation properties of plastic scintillators based on polymethyl methacrylate with various luminescent dyes are considered. It is shown that replacing the naphthalene conventionally used in these scintillators as a secondary solvent with octadeuteronaphthalene and 1,3-divinylbenzene will not alter either their scintillation efficiency and optical transparency, or their thermal, light, and radiation-damage stability; replacing it with 1,1,3-trimethyl-3-phenylindan, however, improves all these characteristics. It is demonstrated that n-terphenyl, 2,5-diphenyloxazole, 2-biphenyl-5-phenyl-1,3-oxazole, 2-biphenyl-5-( α -naphthyl)-1,3-oxazole, 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole, and 2-(4'-tret -butylphenyl)-5-(4''-biphenylyl)-1,3,4-oxadiazole can be used as luminescent activators, and n-bis-( o -methylstyryl)-benzene and 1,4-di-(5-phenyl-2-oxazolyl)-benzene are applicable as wavelength shifters.