CAP toxicity on CAPSand CAPR ES cells as assessed by single point growth curve. 1 × 105 cells were plated into replicate 35 mm wells containing CAPR feeder cells. The ES cells were cultured for 7 days at CAP concentrations of 0, 25, 50, 75, 100, and 150 μg/ml. The cells were then removed and counted. Results are graphed as the concentration of CAP versus the percentage of cell growth relative to growth without CAP selection.