The effect of 50 ppm F as sodium fluoride in the drinking water for 15 weeks on bone, plasma, and urinary cAMP levels, and on bone alkaline and acid phosphatase activities have been investigated in rats stressed with calcium deficiency and/or lactation, as well as in normal rats. Lactation and calcium deficiency (0.1 % calcium in diet) was found to cause an increase in urinary cAMP excretion but did not cause any significant alteration in plasma and bone cAMP levels. Bone alkaline and acid phosphatase activities were lower in lactating rats furnished the 1.0% calcium diet when compared to the nonlactating controls. Fluoride had no effect on all parameters studied.