Fetal bovine serum (FBS) is the most widely used growth supplement for cell cultures, primarily because of its high levels of growth stimulatory factors and low levels of growth inhibitory factors. Maintaining successful and consistent cell fermentations can be difficult, as FBS is a complex natural product and may vary from lot to lot even from a single manufacturer. The quality and concentration of both bulk and specific proteins can affect cell growth. Quality control tools for FBS are relatively primitive and expensive given the complexity of the sample and the large amounts of FBS used. We undertook this study to examine whether proteomics could be used as a tool to analyze the variability of different fermentation processes. We hypothesized that inconsistent cell growth in fermentations could be due to the quality of FBS and that different lots of FBS had varying concentrations of proteins such as growth stimulatory factors, growth inhibitory factors, and/or other proteins that may correlate with cellular growth rate. To investigate whether this was the case, we grew three batches of adult retinal pigment epithelial cells (ARPE-19) using three different lots of fetal bovine serum (FBS-Ia, FBS-Ib, and FBS-II). We found that the growth rate of the culture was significantly and consistently higher in the FBS-II lot. To determine why the other lots promoted different growth properties, we used proteomic techniques to analyze the protein composition of the three lots. We then performed a time course study to monitor specific changes in individual proteins in the fermentation medium. The amount of several extracellular matrix and structural proteins, which are indicators of cell growth, increased over time. Alternatively, components supplied by the FBS addition, such as nutritional-related and cell-spreading-related proteins, decreased over time.