The Afro-Cuban music sound in “Groovin” included a conga, a Cuban-
influenced bass guitar line from ace session musician Chuck Rainey,
and a harmonica part, performed first for the single version by New
York session musician, Michael Weinstein, and later for the album
version by Gene Cornish.

The single became an instant hit in May of 1967, spending four weeks
atop the Billboard pop singles chart, but not four consecutive weeks
because the sequence was interrupted by Aretha Franklin‘s "Respect"
which spent a week at No. 1 in the middle of "Groovin’"’s run. The song
was RIAA–certified a gold record on June 13, 1967.