Quins make four changes to the side that beat Northampton Saints 30-31 last weekend.
Tom Williams starts at full-back, alongside Jordan Turner-Hall and George Lowe who return from knee and ankle injuries respectively.
There is just one change is made in the front row with hooker Joe Gray named to start, with open side flanker Luke Wallace retaining the captaincy.
Meanwhile, Bath will give both experience and youth a chance in the clash with several Academy prospects set to make appearances.
Academy back-row Will Skuse and Guy Mercer are joined by Simon Taylor at the back of the scrum, with Dave Attwood and Dominic Day renewing their second-row partnership.
At hooker, Lee Mears will captain the side, with Anthony Perenise and Charlie Beech either side of him in the front row.
Another Academy player, scrum-half Chris Cook, creates a new half-back partnership with Stephen Donald as Kyle Eastmond and Tom Biggs come back onto the wings.
Michael Claassens is on the bench, and should he be called upon, will make his 150th appearance for the club.
Harlequins: 15 Tom Williams, 14 Seb Stegmann, 13 George Lowe, 12 Jordan Turner-Hall, 11 Sam Smith, 10 Ben Botica, 9 Karl Dickson, 8 Tom Guest, 7 Luke Wallace (C), 6 Joe Trayfoot, 5 Charlie Matthews, 4 Pete Browne, 3 Will Collier, 2 Joe Gray, 1 Mark Lambert.
Replacements: 16 Rob Buchanan, 17 Darryl Marfo, 18 Kyle Sinckler, 19 Sam Twomey, 20 Jack Clifford, 21 Ollie Lindsay-Hague, 22 Louis Grimoldby, 23 Tom Casson.
Bath: 15 Ollie Devoto, 14 Kyle Eastmond, 13 Matt Banahan, 12 Ben Williams, 11 Tom Biggs, 10 Stephen Donald, 9 Chris Cook, 8 Simon Taylor, 7 Guy Mercer, 6 Will Skuse, 5 Dave Attwood, 4 Dominic Day, 3 Anthony Perenise, 2 Lee Mears ( c ), 1 Charlie Beech.
Replacements: 16 Brett Sharman, 17 Alan Cotter, 18 Kane Palma-Newport, 19 Ryan Caldwell, 20 Josh Ovens, 21 Michael Claassens, 22 Tom Heathcote, 23 Semesa Rokoduguni.
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