A many-phased development program is being carried on at Lancaster to provide special and improved multiplier phototubes for a variety of applications. Special emphasis has been given to improving and testing multiplier phototubes for pulse-height resolution. Tubes of different sizes have been ruggedized to permit scintillation counting in unusual operating conditions, such as during rocket flight. New electron-optical arrangements in multiplier phototube structures have resulted in less transit-time dispersion. Very wide spectral response has been obtained by use of the multialkali photocathode in a fused silica envelope. Plans for work in the next year include further development of very-high-speed multiplier phototubes capable of pulse rise times in the 10-10-second range, and further expansion of the RCA line to include tubes of other sizes, tubes with lower dark current, and tubes with extended ultraviolet response.