The saints include Saint Jerome (with his lion) and Saint Joseph (with his flowering staff).
The original destination of this altarpiece was probably a chapel or Franciscan church dedicated to Saint Bernardino, who is shown with his monogram of the name of Jesus (IHS) and three mitres at his feet. The mitres are inscribed with the three bishoprics of Urbino, Siena and Ferrara which the saint refused to accept.
Also represented are Saint Francis (showing his stigmata), Saint Nicholas of Bari (holding three gold spheres), Saint Catherine of Alexandria (accepting a ring from Christ, in allusion to her vision of a 'mystic marriage'), and Saint Clare holding the monstrance.
From The National Gallery Podcast: Episode Twenty Six, December 2008