1. The injection of fresh saline suspensions of ox pituitary produces a prolonged fall in the calcium content of the serum of normal female rabbits and rabbits deprived of their ovaries.
2. After sexual excitement there is a fall of blood calcium in the female rabbit beginning within 4 hours from association with the buck, followed by a secondary rise at the time when ovulation occurs with a further fall subsiding by the time the corpus luteum is fully formed.
3. The removal of the ovaries from sexually mature rabbits does not produce any significant change in the calcium or magnesium level of the serum.