Amphiphilic block copolymers based on hydrophobic polysulfides (poly(propylene sulfide), PPS) and hydrophilic polyethers (poly(ethylene glycol), PEG) have been used to solubilize and disperse single-walled carbon nanotubes (SWNTs). The obtained highly concentrated aqueous dispersions are stable for months. The factors that affect the dispersant activity of the studied block copolymers have been characterized, and comparisons with the much more investigated oxygen analogues (Pluronics) are reported. The biocompatibility and the stability after dilution of the most representative suspensions have been investigated as prospective drug carriers.