The influence of a nonionic surfactant (Triton X-405) on the adsorption behavior of single-stranded oligodeoxyribonucleotide (poly(thymidylic acid) (dT(35))) Onto cationic aminated polystyrene latex particles has been investigated. A preliminary study was performed on the adsorption of Triton X-405 onto these cationic particles, showing a maximum amount of similar to 0.5 mg m(-2) at the plateau. Desorption of the nonionic surfactant even after an extensive cleaning procedure was not completed, indicating that probably low HLB (hydrophilic and lipophilic balance) species were still strongly adsorbed. The modification of the electrophoretic mobility of the latex particles together with the slight decrease in the colloidal stability suggested that the residual Triton X-405 molecules would adopt a flat conformation at the particles surface. Then, the adsorption behavior of dT(35) onto precoated cationic latex was thoroughly examined under various conditions and compared with the case of bare latex particles. It was clearly evidenced that the residual adsorbed amount of nonionic surfactant significantly affected the surface nature, especially at basic pH. It was interesting to notice that dT(35) adsorption was strongly reduced at basic pH and that its desorption was favored using basic pH buffer containing Triton X-405 and high ionic strength. Kinetic exchange experiments were also performed using labeled P-32-dT(35) and unlabeled dT(35), indicating that the exchange took place with no marked differences between coated and bare latex particles.