We have examined the adsorption of poly (ethylene oxide)/poly (propylene oxide)/poly(ethylene oxide) (PEO/PPO/PEO) triblock copolymers (Pluronics)(TM)) on dimethyldichlorosilane-treated glass (DDS-glass). The surface concentration of I-125-labeled Pluronic F-68(76/30/76) reached a maximum of 0.3 mug/cm2 when the bulk concentration in the adsorption solution was 3.0 mg/mL. Above 5.0 mg/mL, the surface Pluronic F-68 concentration started to decrease and reached 0.17 mug/cm2 when the bulk concentration for adsorption was 10 mg/mL. The surface concentration of Pluronic F-108 (129/56/129), on the other hand, increased to 4.0 mug/cm2 at the same bulk concentration. Fluorescence spectroscopic studies using pyrene suggested that the Pluronic F-68 molecules self-associated at the bulk concentration of 5.0 mg/mL and above. Because the aggregates are expected to expose the hydrophilic PEO segments to water, they may have lower affinity to DDS-glass. Aggregation of Pluronic F-68 also decreases the number of individual Pluronic molecules for adsorption. Pyrene fluorescence in Pluronic F-108 solution, however, suggests that Pluronic F-108 molecules do not form aggregates. It appears that the high surface concentrations of Pluronic F-108 may result from the preferential adsorption of individual molecules in multilayers. This explains the high effectiveness of Pluronic F-108 in preventing protein adsorption and platelet adhesion when adsorbed on to the hydrophobic surface.