Limestone was crumbled into fine particles (LF) of 0.1-0.4 mm or to a particulate grit (LG) of 2-4 mm. One hundred and eighty individually kept Hy-Line Brown laying hens were used in the experiment and divided into 10 groups. Diets containing 8.1% of LF or LG substituted for LF at a proportion of 10, 20, 40, 50, 60, 80 and 100% were compared with diet containing 8.1% oyster shells. At moderate substitution levels, the particulate limestone grit increased the thickness of eggshells in the first laying period (60-80% LG), improved yolk pigmentation (20-100% LG) and enlarged calcium deposition in eggshells (10-100%) LG). Partial (20-90%) and complete substitution of LG for LF increased eggshell breaking strength, but improvement of tibia bone strength was observed only at 20% LG limestone. Analysis of feed refusals suggests that the limit value of voluntary intake of grit particles LG is 5.5 g daily per hen.