Decay of biotin-x-N-hydroxysuccimide ester–labeled erythrocytes. The percentage of labeled cells (day 0, set to 100%) was measured every 3 to 4 days until less than 0.5% labeled cells was found and the data were plotted against the day of sampling. For each individual mouse, an exponential regression equation was determined that was used to calculate the erythrocytes' half live as shown in the figure. Life span of tg6 erythrocytes is reduced to almost a third compared with wt erythrocytes. Means ± SD; n = 5-6.