IN 1979, three veteran Mississippi blues musicians -- guitarist Jack Johnson, harmonica and keyboard player Frank Frost and drummer Sam Carr -- recorded an album called "Rockin' the Juke Joint Down." The music rocked all right, but in a relaxed, old-fashioned and thoroughly uncomplicated way. In fact, the Jelly Roll Kings, as the trio was dubbed, sounded as if they hadn't listened to anything but Roadhouse blues and old country tunes for the previous 20 years, much less been influenced by it.

Now comes the follow-up: Big Jack Johnson's "The Oil Man," which reunites Johnson and Frost in a similar down-home setting. The intervening years, however, have wrought some changes. For one thing, Carr has been replaced on the album, and his slapping rhythms have given way to a tighter, more modern beat. Moreover, because Frost plays the keyboards exclusively this time around, gone are the piercing cross-harp riffs that often recalled his mentor, Sunny Boy Williamson.

But as the title indicates, this is really Johnson's album, and he makes the most of it. His fat, reverb-drenched guitar tone and convincing vocals make for a potent combination on such classics as "Catfish" and "How Many More Years," and even help to compensate for such obviously derivative songs as "I'm Gonna Give Up Disco" (a thinly disguised rewrite of Jr. Parker's "Mystery Train"). Also worth hearing are Johnson's delightfully distinctive treatments of "Steel Guitar Rag" and, oddly enough, "Tom Dooley."

Incidentally, Frost's performance in the recent film "Crossroads" has led to the reappearance of the band's 1979 release. With its steady-rolling rhythms and old-timey blend of shuffles, blues and novelty tunes, this is certainly the best place to get acquainted with the Kings. Not only does it feature Frost on harmonica and Carr on drums, but the performances radiate great warmth, honesty, spirit and humor. BIG JACK JOHNSON --

"The Oil Man" (Earwig 4910).

JELLY ROLL KINGS --

"Rockin' the Juke Joint Down" (Earwig 4901).

Johnson, Frost and Carr appear at Twist & Shout (at the Bethesda American Legion) Saturday and at Quincy's in Arlington Sunday.