The electrophoretic mobilities of curved and normal DNA molecules of the same size have been measured in polyacrylamide gels containing various acrylamide concentrations and cross-linker ratios. Ferguson plots were constructed to extrapolate the observed mobilities to zero gel concentration. The DNA samples were two 147-bp restriction fragments, called 12A and 12B, obtained from the Mspl digestion of plasmid pBR322, and head-to-tail multimers of each fragment. Fragment 12A is stably curved and migrates anomalously slowly in polyacrylamide gels; fragment 12B has the conformation of normal DNA and migrates with normal electrophoretic mobilities. The extrapolated mobilities of the curved fragment 12A and its multimers at zero gel concentration are lower than the extrapolated mobilities of the normal fragment 12B and its multimers. The free solution mobility of the curved fragment 12A, measured by CE, is also lower than that of the normal fragment 12B. The combined results indicate that the extrapolated mobilities observed for curved DNA molecules at zero polyacrylamide gel concentration reflect the intrinsic differences in their free solution mobilities.