Uncoated single‐strands DNA mixed with BAC (benzyldimethylalkylammonium chloride) were deposited on gold substrates and imaged in air with Scanning Tunneling Microscopy (STM). Constant‐current and gap‐modulated STM images showed that most of the DNA filaments tend to form aggregates where it is difficult to distinguish among the different nucleotides. Along isolated filaments small structures that we have, tentatively, assigned to phosphate and sugar groups, are present; bumps in a hexagonal configuration, that correspond presumably, to the nucleotides of DNA, have sometimes been observed.