Mammalian cell culture technology has been used to produce structurally complex protein molecules and to construct devices for tissue engineering applications. This study investigated the cultivation of Chinese hamster ovary (CHO) cells on Cytodex I microcarriers in a spinner flask. The initial cell attachment was rapid with a rate constant of 5.56 x 10(-2) min(-1) under the condition of continuous stirring at 40 rpm using 2 g l(-1) of the microcarriers in a DMEM/F12 (1:1) medium. Adding serum to the medium decreased the rate of cell attachment in a dose-dependent manner. In contrast, the cell growth rate and maximum cell density increased with a shorter lag phase as the concentration of serum in the medium rose. To reduce the cost of the cell culture, the surfaces of Cytodex 1 microcarriers were immobilized with insulin using an adsorption-drying method and then used for the cultivation of CHO cells in a serum-free medium. The growth rate of CHO cells on insulin-immobilizpd microcarriers using a serum-free medium was comparable to that on untreated microcarriers using a 2% serum-containing medium. In addition, insulin immobilization also enhanced the value of the growth yield for glucose (Y-cell/glucose) from 2.41 x 10(5) to 3.66 x 10(5) cells mu mole(-1). This finding suggests that the immobilized insulin promoted glucose utilization, thereby enhancing cell growth. The immobilization of insulin on microcarriers is, thus, highly recommended to improve the outcome achieved in a serum-free culture.