The performance of J.S. Bach's Passion According to St. John at Sanders Theater has become almost an annual affair. The Passion was originally performed as a liturgical drama around Easter, but it has lost some of its religious connotations through the centuries and is now a staple in choral repertoire. Saturday night the Cecilia Society, an outstanding local chorus, celebrates its 100th anniversary with a performance of the Passion featuring some of Boston's finest vocalists on the solo parts. Backing up the singers will be the Cambridge Festival Orchestra. 8:30 p.m. Tickets available at the door.

Saturday

DUNSTER: Tanya Bartevyan Gailus '77, pianist, performs works of Beethoven, Chopin and Charles Kletzsch, resident music librarian. Dunster Library, 5:30 p.m.

Sunday

ELIOT: James Madilena, bass, and Georgeann Peterson, piano. Eliot House Library, 8 p.m.

Monday

The Concord String Quartet (courtesy of the Fromm Music Foundation) presents A Program of Contemporary Music with Scott Nickrenz, viola, as guest artist. Sanders Theater, 8:30 p.m. Free.