The Bost Building is significant under National Historic Landmark Theme V 5 (Developing the American Economy: Labor Organizations and Protests). It is the primary extant resource associated with the 1892 Battle of Homestead. It was the headquarters for Amalgamated Association of Iron and Steel Workers in Homestead and for the Advisory Committee representing eight local AAISW lodges, as well as the base for the newspaper correspondents from this country and Great Britain who were expecting, and witnessed, a major confrontation between capital and labor. The period of significance is June 29, 1892, when the workers were first locked out of the Homestead Steel Works of the Carnegie Steel Company through November 21, 1892, when the Amalgamated official ended the strike and its Advisory Committee vacated the Bost Building. It includes the bloody events of July 6, 1892, the date of the Battle of Homestead.

The Bost Building has high integrity, especially on the third floor, where the union was headquartered during the 1892 strike and lockout. The floor plan is virtually intact and the original plaster and lathe walls are unaltered, as are the high ceilings, original window and door arrangements most of the sash, and nearly all of the interior trim. Stove pipe covers indicate the location of the stoves that heated the rooms. The floor plan is as original on the second floor, with its distinctive double stacked corridor. On the stairway landings is the graffiti made at the time of the July events. The first floor has its pressed tin ceiling and bead board paneling. As period photographs show, the exterior appearance has not been modified except at the storefront, which is hardly surprising given the building's location in Homestead's commercial district. Interior changes since the building's 1892 construction have been superficial and are easily reversible. A room on both the second and third floors has been partitioned to add bathrooms. For fire code purposes a wall has been added at the top of the third floor staircase and door frames (all lacking doors) have been erected in some hallways. They can easily be removed, as can the paneling and drop ceilings added to a small percentage of rooms. The Bost Building retains the design and feeling that it had when it served as the Amalgamated's headquarters during the pivotal days of July 1892. - National Historic Landmark Nomination, 17 March 1998