A new pathway for the radiolabeling of Pluronic PE6800 was developed. In a first step, the CH2-OH end groups of the copolymer were substituted by tosylates; in a second step these were reduced by [H-3]-NaBH4 to obtain tritiated chain ends. The final product was shown to be a mixture of native, tosylated, and reduced Pluronic containing I tritium atom per 1110 Pluronic molecules. The labeling procedure did not affect the molecular weight distribution nor the adsorption isotherm of the copolymer on polystyrene plates. A plateau value of about 0.7 mug/cm(2) is reached at a concentration in solution of 500 mug/ml, i.e., much lower than the cmc. Upon drying, the Pluronic adsorbed layer reorganizes in particles with a size of about 30 to 60 nm which cover about 15% of the substratum surface. This observation is of great importance for the design of protein-resistant surfaces by adsorption of Pluronic. (C) 2003 Elsevier Science (USA). All rights reserved.