The Wainwright Building is the most important skyscraper designed by Sullivan

The most significant skyscraper Sullivan created is the St. Louis 10-story Wainwright Building, which is one of the most interesting facts about Louis Sullivan. It is entirely made of steel, a design proposed by William Le Baron Jenney in Chicago between 1883 and 1885. In contrast to the Auditorium Building, which has complete masonry external walls that are load bearing, the idea was developed there. Jenney and others frequently turned to inappropriate historical aesthetics because they were unable to convey the height of a tall building visually. However, Sullivan tackled the issue head-on and created a "proud and soaring" unity in his design.

He gave his structure a two-story base, stressing the vertical features above it while minimizing the horizontals because they are recessed. A thick ornate frieze and a projecting cornice top these vertical beats. The 16-story Guaranty (now Prudential) Building in Buffalo, designed by Adler and Sullivan, is comparable, with the exception that ornamental terra-cotta covers its outside rather than red brick. The two structures rank among the outstanding creations of Adler and Sullivan.