Static and dynamic light-scattering experiments were performed to study the association behavior of a BEB-type (B and E represent poly(oxybutylene) and poly(oxyethylene), respectively) triblock copolymer, B(5)E(91)B(5), in aqueous solution from dilute to concentrated solution regions over a range of temperature (15.5-45.0 degrees C). B(5)E(91)B(5) is soluble in water at low temperatures. At 15.5 degrees C and concentrations below 3% (w/v), only unimers are present. At higher temperatures and in the dilute solution region, the degree of association and the aggregation number increase, while the critical micelle concentration decreases with increasing temperature. The existence of branched associated structures is suggested in the concentrated solution region, where interconnected micelles are in coexistence with small molecular associates (or premicelles) and the average size of these interconnected micelles appears to increase with increasing concentration.