Bovine liver catalase immobilized on eggshell particles was characterized and the reusability of the immobilized catalase was investigated in a batch type reactor. For immobilized catalase onto ground eggshell (ICATG), the optimum initial amount of catalase was 85 mg g(-1) of eggshells, the optimum pH was 6.0 (75 mM citrate buffer) and the temperature was 30 degrees C. The V(max) and K(m) values of ICATG were determined as 29.1 +/- 1.2 U/mg of protein and 41.9 +/- 2.7 mM, respectively. The reusability of ICATG was tested and the remaining activity of ICATG was found to be 73 % of the initial activity after 80 cycles of batch operation. The amount of catalase bound onto the carrier was estimated by using the results of induced coupled plasma measurements. The catalytic efficiencies (k(cat)/K(m)) of free catalase and ICATG were found to be 1.4 x 10(6) and 2.8 x 10(3) dm(3) s(-1) mol(-1), respectively. Catalase immobilization onto eggshell is economic and has good reusability. Hence, it can be concluded that eggshell is an efficient carrier for immobilizing catalase.