With polish, grace and skill, the Harvard-Radcliffe Callbacks showed a packed Sanders Theater crowd how to have a good time on a Saturday night without musical instruments. In typical fashion, the group performed a wide variety of songs, traditional and modern, and performed them consistently well. Although the crowd seemed a touch restless during the opening acts, the Callbacks put on a jam that would satisfy even the strongest desire for an a capella fix.

The traffic jam commenced, appropriately enough, with the number "Traffic Jam," featuring strong singing and slammin' raps from Matthew Briones.

This introduction, brash enough to cause riots, was tempered by the smooth melodies of Elvis Costello's "Veronica," performed by Daniel Brotman and Gordon Woodward.

First-year Roy Hamilton showcased his talent in a touching rendition of "Over the Rainbow." And Jessica Walling's solo in the song stirred among the crowd a nostalgia for those days back in Kansas. Never in his many days on the a capella beat has this reviewer felt such an emotional bond with the audience.

If by some jest of Providence, the first three numbers did not provide fun enough for the crowd, the group's thickly textured "Leave It" put to rest any lingering doubts as to the sweetness of this jam.

After that moment of a capella regeneration, Jennifer Light's solo in "I Want a Monster" added a crucial element of demented wackiness to the jam, and Emeline Brown's soprano in "The Circle Game" drew hoots of appreciation from a crowd tingling with delight.

Successive songs only added to this powerful display of talent. "Poison Ivy," featuring Gordon Woodward's polished solo, took the audience back to the early days of rock 'n' roll; and "Ain't Misbehavin'," featuring a solid solo from Jennifer Hunter, proved that jazz is not above the Callbacks' ken.

After the signature song, "Old Irish Blessing," the concert reached a critical juncture. Had the traffic jam ended on a mediocre note, the crowd would have experienced great pains of unfulfilled expectation. But if the jam ended on a high note, the crowd would witness one of the best moments of this young Harvard a capella.

Under this kind of existential pressure, bad boy James Beckerman came through with an inspired rendition of "Drift Away." Not only did his deep, sexy voice oblige the crowd to run for cold showers after the concert, but his soulful performance also answered that age-old question: can the audience ever keep the beat? Yes, sometimes they can.

With a shrieking crowd shaking Sanders Theater, the Callbacks added two impressive encores to the evening's list of memorable performances. "Flappers," featuring a dapper Craig Peters and a scatting Roy Hamilton, left the audience tapping their feet and humming along, even though most did not know the tune. Peters and Tanya Fenmore also gave the crowd a quality dance routine, proving that the Kroks do not have a lock on tap dancing.

The final encore featured Lane Addonizio in "Straight to my Heart." Addonizio's riveting performance went straight to the crowd's collective heart.

In addition to delivering stirring musical performances, the evening boasted topnotch humor. The Callbacks presented sharp parodies of "Beverly Hills 90210" and MC Hammer's Pepsi commercial, and the emcees for the evening, Faith Salie and Nell Benjamin, were hilarious.

The opening acts provided the only negative moments of this jam. The Yale Baker's Dozen typified everything that can be vapid about a capella music. But even they had their moments-the group gave a particularly memorable rendition of Gershwin's "Summertime." Unfortunately that smattering of praise cannot be bestowed upon the Wellesley Widows. There was nothing redeeming about their performance-the group would have better entertained the audience by remaining in their part of Massachusetts.