Abstract: A structural gasket system for curtain walls and the like in building structures has intersecting mullions with T-shaped outer ends (28, 128, 248) or mullions with enlarged outer ends (328, 358) joined at the intersecting joints, integral elastomeric gasket members (48, 226, 344) surround the outer ends of the mullions, including the T shapes (42, 142, 264) or the enlarged ends (340, 366), and retainers (62, 150, 240, 302, 372) engage each side of the mullions and lock the gasket members to the mullions. The gasket members have laterally-extending inner and outer lips forming channels the width of panels (26). The retainers (62, 150, 240, 302, 372) bear against the inner lips (56, 236, 368) of the gasket members to seal the gasket members to the panel. The structural gasket system can be installed from the inside of the building and insulates the mullions from the outside.