An in situ study of the microstructure and mechanical properties of polystyrene-poly(ethylene-butylene)-poly styrene (SEBS) triblock copolymer gels was performed. Simultaneous time-resolved synchrotron radiation X-ray scattering and stress-strain measurements at extensions up to lambda = 2 indicate that the macroscopic deformations are transferred to a microscopic level via the threedimensional network of microdomains. The deformation of the microstructure is nonaffine at low extension rates (4 x 10(-4) s(-1)) and becomes affine at higher rates (10(-2) s(-1)).