The two movements realize their sonata forms in similar ways. Both movements use a primary theme (P) in C minor and a secondary theme (S) in E-flat major. This is no surprise, as most C-minor sonata movements do this. However, there are other less common resemblances. The P theme and the transition (Tr) sections are almost exactly the same length in terms of numbers of measures, and both insert a four-measure thematic introduction between the slow introduction and the start of the P theme, as indicated with the formal diagram below.
Lastly, each movement has a four-measure portion around the middle of its E-flat-major S theme that sounds very similar to the other, as shown below. (This portion's place in the form of each movement is indicated by the enclosure in the graphic above.) Both portions are soft, and both use alternating and echoing one-measure motives that involve the wind instruments of the orchestra. These motives essentially embellish upon a Bb-F-Bb-F treble succession. The harmony and bass line below this treble succession is the same in each portion, prolonging a first-inversion tonic triad, a standard "beginning-of-the-end" chord for a secondary theme. However, in characteristic fashion, Brahms displaces the harmonic rhythm from the barline.