The effects of various drugs on the structure of a bent DNA fragment have been investigated by studying DNA mobility in polyacrylamide gels. This DNA fragment has an anomalously slow rate of migration on account of its phased runs of adenines. Nogalamycin and echinomycin increase the gel mobility of kinetoplast DNA suggesting that the bending has been removed. Mithramycin, actinomycin, distamycin and ethidium have either no effect or cause a further reduction in mobility. These results are compared with other, non-bent DNA species which always show a decrease in gel mobility in the presence of DNA binding drugs.