It was released soon after Allan Clarke, who was featured on lead guitar as well as lead vocal had left the group, from their album “Distant Light” (1970). As the group had just left EMI/Parlophone and signed with Polydor, they did not promote the song. However it became a No. 2 hit in the United States, their greatest ever singles success there. It was inspired and in the style of the rock and roll group Creedence Clearwater Revival, and on being reactivated by EMI in Britain a few months later, it reached No. 32.
The song is notable in that it features Clarke playing rhythm guitar, something he rarely did (Clarke came up with the song’s signature guitar rhythm that opens the song).
Taken from: http://en.wikipedia.org/wiki/Long_Cool_Woman_in_a_Black_Dress