Abstract: A guide line clamp supports a guide line in an alignment slot to accurately position the line. The clamp includes a releasable clamp body having a groove and a manually operable lever for closing a jaw onto a structural supporting flange of a T-shaped member for a drop-in panel ceiling. A guide line body extends from the clamp body and includes the alignment slot which is perpendicular to the groove and has a base aligned with the clamping surface of the groove. The inner end of the slot splits and extends laterally to the sidewalls. An offset line clamp plate is secured to the bottom of the guide line body and defines an encircling and laterally offset recess having inclined walls within which the line is wrapped and releasably gripped. The plate has edge openings for the end of the line.