Quins have mounted an impressive march into title territory, which was highlighted by their victory over Bath last weekend.
Bristol though, have been lifted by the recent return from injury of key figures like scrum-half Shaun Perry and back-row forward Dan Ward-Smith.
And Bristol assistant coach Paul Hull said: "Those guys are hungry to play because they haven't played for weeks.
"That has given us a really big lift, and hopefully, the impetus to go and make it three wins from three.
"Dean Richards has got a good squad at Harlequins, and he has them playing well. They have good physicality and they play hard, something he has brought to Harlequins from Leicester.
"They started well this year, but then had a little blip which was when we played them in the Heineken Cup. But now they are coming back to form, and it is going to be an interesting battle."
Bristol have made five changes from the side that easily beat Newcastle last time out, with centre Neil Brew, wing David Lemi, prop Alex Clarke, lock Nathan Budgett and flanker Andrew Blowers all gaining starts.
Richards though, keeps alterations to a minimum, replacing an injured Ugo Monye at centre with Hal Luscombe, and giving lock Ollie Kohn an opportunity instead of the rested James Percival.