Direct force measurements of the interaction between silica surfaces in low concentrations of the soluble cationic surfactant cetyltrimethylammonium bromide reveal a long-range strongly attractive hydrophobic force extending out to 100 nm. Similar forces observed for cetylpyridinium chloride in 0.1 M electrolyte demonstrate that the hydrophobic attraction is undiminished in the presence of concentrated electrolyte. These results are discussed in relation to other investigations of the long-range hydrophobic attraction and lead to the conclusion that electrostatic double layer forces are unable to account for these attractive forces.