The adsorption behavior of the novel type of water-soluble amphiphilic triblock copolymers PGMA-b-PPO-b-PGMA at the air water interface is studied by tensiometry and monolayer techniques. In particular. (PGMA(14))(2)-PPO34 is found to be strongly surface active (Pi(max) similar to 38.1 mN/m, cmc similar to 50 mu M). in spite of having a relatively short hydrophobic PPO middle block. Time-dependent adsorption measurements exhibit two different types of adsorption kinetics depending on concentration. Monolayers deposited by spreading form pseudo-Langmuir films, in spite of (PGMA(14))(2)-PPO34 high water solubility. The transition from a dilute to a semidilute regime during compression of the monolayer occurs at a mean molecular area around 4424 angstrom(2)/molecule (Pi = 0.03 mN/m). Above Pi = 2.1 mN/m (1291 angstrom(2)/molecule) PGMA segments begin to change from a flat two-dimensional conformation to loops and tails protruding into the subphase. The onset of the conformational change for PO segments takes place at a mean molecular area of similar to 625 angstrom(2)/molecule (Pi = 15.5 mN/m). In the range Pi similar to 21.4-23.8 mN/m the PPO blocks adopt a three-dimensional conformation. A new methodology for the estimation of the amount or polymer absorbed at the interface (Gamma) as a function of the solution hulk concentration from tensiometry measurements in pseudo-Langmuir spread films is proposed. The obtained adsorption isotherm suggests the occurrence of a conformational change of the PPO block segments toward conformations having smaller molar areas for actual bulk concentrations above 6.0 x 10(-8) M. The surface tension versus polymer bulk concentration curve (gamma vs In C) exhibits a sharp break at low concentrations, which is probably due to a conformational change within the adsorbed layer. A theoretical multiple conformation model reproduces satisfactorily the experimental dependency of surface pressure on polymer adsorption (Pi vs Gamma) at low and intermediate ranges of polymer concentrations in the solution hulk. A ratio of approximately eight between the average molecular areas it low coverage and at full coverage confirms that (PGMA(14))(2)-PPO34 chains are highly flexible and able to adopt very different conformations during, the transition of the adsorbed polymer film from a highly diluted to a nearly saturated state. There are some experimental indications that nonequilibrium effects might determine a bimodal conformational distribution within the adsorbed (PGMA(14))(2)-PPO34 layer, which departs substantially from the equilibrium adsorption picture.