MICKEY MOUSE has left the building. That is, left the marquee over the World of Disney Store on Fifth Avenue at 55th Street, where he, Minnie and Pluto guarded the entrance for well over a decade. They were removed earlier this year, after Disney moved out.

What’s left is a big, conservative limestone office block built in 1927, home until 1933 to the radically modern headquarters of NBC.

The developer Floyd Brown began work on the 15-story office building, at first called 711 Fifth Avenue, in mid-1926. At the end of the year Mr. Brown announced that the new National Broadcasting Company would be leasing the upper floors for its offices and broadcast studios. By that time the exterior design must have been set, and so it must reflect Mr. Brown’s tastes.

An architect, he founded the Bethlehem Engineering Company in 1918 to develop and design structures; only Bethlehem’s name appears on the NBC drawings.

Even on Fifth Avenue, a full limestone facade is sumptuous for a commercial structure, and Mr. Brown gave it a double-height second floor designed for a bank tenant, with a giant colonnade on both street elevations. Above that his building is not much to look at, just window punch-outs and a few setback floors with some detailing.

The pseudonymous critic T-Square, writing about the building in 1927 in The New Yorker, commented that “No matter what the modernists say — or do — there is no getting away from the fact that a Corinthian column is a swell thing.” However, he did note that the essence of the new structure was “economy and simplicity.”

For the design of its offices, NBC, established only in 1926, retained the provocative urban theorist Raymond Hood. He told The New York Times in April 1927 that he was unhappy with the drabness of typical recording studios, and certain that such surroundings affected performers negatively.

Thus, The Times reported, he was designing the various studios as a Gothic church, the Roman forum, a Louis XIV room and, in a space devoted to jazz, something “wildly futuristic, with plenty of color in bizarre designs.”

However, photos of the finished interiors show uniformly modernist designs, although tempered by traditional motifs. For instance, a sinuous strip of Art Deco wall painting is based on the Vitruvian wave, a pattern dating back to the classical period. Some peculiar bundled light fixtures are topped by anthemion leaves, another classical allusion.

The lighting was dramatic and copious; in 1928 The Architectural Record quoted Mr. Hood as explaining that it did the work of an audience, helping to keep a performer alone in a studio “keyed up to a high pitch.”

The broadcast studio was a new problem in architectural design, and rooms had to be soundproofed in ways hitherto not considered. There were separate air ducts for each studio, with interior baffles and special flooring. The broadcast facilities in NBC’s building were the most advanced in the country.

The broadcast network, too, was a new idea. The established pattern was for local stations to generate their own programming, all live. Thus, New York-area show listings in The Times on Armistice Day 1927 included the dedication of the Canadian monument at Arlington National Cemetery on WEAF (one of two NBC stations), French lessons by V. Harrison-Berlitz on WNYC, farm market reports on WJZ (the other NBC station), “The Smiling Baritone” on WOR, and the Beaux-Arts Orchestra on WABC. Somehow the radio industry was able to function without vulgar language and incendiary political insult.

The development of NBC and other networks promised economies of scale. There was no reason that WGY in Schenectady had to pay the local Van Curler Orchestra if it could just take an NBC feed. In such a calculation, Van Curler became just another fungible content provider.

At first, major artists resisted appearing on the radio, believing that their concert fees would be reduced or that their voices would be presented in an unflattering way. In 1928 after an initial radio appearance, the pianist Ignace Paderewski announced that he would never play for broadcast, according to The Times.

But in the same year the soprano Amelita Galli-Curci changed her mind and performed on NBC. In 1929 the band leader John Philip Sousa also reversed his position and broadcast from the NBC building. His decision was perhaps influenced by his fee, in excess of $50,000; NBC said it spent over $5 million on talent in 1928.

In 1933, having outgrown 711 Fifth Avenue, NBC moved to Rockefeller Center, sometimes called Radio City at the time. After that, its old home was repeatedly altered. Patricia Maes, a vice president of Jones Lang LaSalle, the managing agent, says only scraps are left of Mr. Hood’s remarkable design.

Disney opened on the ground floor in 1996 and installed the bronze-toned sculptures over the Fifth Avenue entrance. But now they are gone and the space is for rent. Zoraya Suarez, a spokeswoman for Walt Disney World, says mice and dog are bound for Florida — snowbirds like so many New Yorkers.