Powdered chicken eggshells might be an interesting and widely available source of calcium. In two studies using piglets we determined the digestibility of calcium from different diets. The first study compared casein-based diets with CaCO3 (CasCC) or eggshell powder (CasES). The second study compared soya protein isolate-based diets with CaCO3 (SoyCC) or eggshell powder (SoyES). Diets were fed to groups of six piglets. Faeces were collected quantitatively. No adverse effects of eggshell powder were observed with regard to magnesium and crude fat digestibility. Calcium from eggshell powder was more digestible than calcium from purified CaCO3. In the first study, digestibility coefficients for calcium were 66.9 (SD 7.9)% for CasCC and 71.3 (SD 3.8)% for CasES. In the second study, these coefficients were 46.7 (SD 8.6)% for SoyCC, and 65.9 (SD 3.7)% for SoyES, a significant difference. Our conclusion is that eggshell powder is, in the case of casein-based diets, as good a source of calcium as CaCO3 and, in the case of soya protein-based diets, better than CaCO3 for growing piglets. As the piglet model is considered to be representative for humans, chicken eggshell powder is also a promising source of calcium for human nutrition.