No breakage of femoral prosthesis stems made of hot-forged cobalt-base or titanium-base alloys has been reported since 1972, in spite of their being loosened and severely overstressed. The minimum requirements imposed on fracture-resistant femoral prosthesis stems were established in laboratory tests and studies lasting several years. The results of these time-consuming and costly efforts have been confirmed by the nonoccurrence of fatigue fractures in more than 350 000 original Mueller and Weber hip joint prostheses with stems made of hot-forged, high-strength Co-Ni-Cr-Mo Protasul-10 alloy, one of the future-oriented alloys used for biocompatible and highly stressed long-term implants. Straight-stem hip prostheses made of hot-forged Ti-Al-V alloy in combination with ceramic Biolox ball heads give promising results, as has been demonstrated by extensive laboratory tests. This must be further confirmed, however, in long-term field studies.