The use of an elemental source molecular-beam epitaxy (MBE) machine for the growth of phosphides requires hardware and operating procedures different from those normally encountered in the growth of arsenides. The main hardware alterations are the use of valved group V cracker sources and different pumping schemes. Operating procedures must be developed to cope with higher operating pressures and flammable deposits. High-quality phosphides and abrupt arsenide/phosphide interfaces are now possible using elemental source MBE.