Mice fed the Osborne, Mendel and Park diet, containing a low P-high Ca salt mixture, develop rickets as early as 7 days, with evidence of healing about 28 days. Those fed on the Steenbock-Black diet 2965 also developed rickets at 7 and 14 days, with healing at 20 and 27 days. Osteoporosis was present in many cases, especially after healing had taken place.