To study the effect of Fe(2+) on the cell culture, preliminary experiments related to the lipid peroxidations of 3T3 cells and calf serum were carried out. Amonuts of lipid peroxides, as thiobarbituric acid (TBA)-reactive substances, were measured by means of the TBA color reaction under the acidic conditions by acetic acid, and were expressed as TBA value. The TBA value of calf serum in the phosphate buffered saline (PBS) with ethyrendiaminetetraacetate (EDTA) was lower than that of the control. The value in the presence of Fe(2+) showed significantly high level, but it was almost prevented by the addition of EDTA. Besides, Fe(2+)-induced lipid peroxides of serum in the PBS during the incubation at 37℃ were capable to measure by the application of EDTA. The TBA values of trichloroacetic acid (TCA) precipitates isolated from serum in the PBS and the culture medium were lower than that of control serum, but no difference was observed between the both TCA precipitates. The results suggested that the impurities in the culture medium were removed by TCA precipitation. Effects of Fe(2+) and EDTA on the TBA value of TCA precipitates were observed similarly to the case of control serum. Fe(2+)-induced lipid peroxidation of the cells in the PBS, which the peroxidation was stopped by the addition of EDTA, was observed, and it was accompanied with the lag time of induction period. The TBA value of the cells was more prevented by EDTA. The method in this paper may not be capable for the quantitative measurements of lipid peroxides in cells or serum, but is applicapable to measure the changes of relative amounts of lipid peroxides.