Hens were given supplementary calcium in the form of 5.7% dietary limestone or oyster shell ad libitum separately from the diet. The two calcium sources were given as supplements to four different diets; wheat-based diets containing soybean meal (SBM) or rapeseed meal (RSM) as the source of supplementary protein and either tallow or corn oil as a fat supplement. Over the 20 weeks of the experiment there were no differences in the rates of production of the birds among the eight experimental treatments. Yolk weight was reduced when the hens fed the diets with tallow as the supplementary fat received their supplementary calcium as oyster shell. When the 5.7% of supplementary limestone was exluded from the weight of feed consumed by the hens given all their calcium mixed into the diet, there was no difference in the amount of feed consumed by the birds on the two systems of calcium feeding. The efficiency of feed conversion to egg meat production was likewise similar for both systems of calcium feeding under the different dietary treatments imposed. Regardless of the composition of the diet, shell weight per unit surface area was greater for the eggs laid by the birds fed oyster shell. (