Filtering single nt mismatch sequences from repertoire data. To determine the extent to which errors could be purged by filtering sequences with single nt mismatches, we examined the residual percent of erroneous sequences for each sequencing reaction after culling single nt mismatch sequences. Assessment of residual erroneous sequences was performed at multiple cutoff values for the frequency of the mismatch sequence relative to the true 5C.C7 (A), OT-1 (B), or DO11.10 (C) sequence, and mean + 1 s.d. plotted. Our data suggests values of less than 0.01 are adequate for optimal error reduction. In application, a cutoff would need to be selected that optimizes removal of erroneous sequences while also minimizing inadvertent culling of true sequences.