A world premiere by Samm-Art Williams is a notable event. Mr. Williams has himself been notable since his heart-filling "Home" won a 1981 Tony nomination and later enriched the stage at the Pittsburgh Public Theater. He's been busy writing for TV, but now he has chosen the August Wilson Center to stage the premiere of "Last of the Line," a comedy with resonance.

That's because, although some of the recent ranting may make us forget, we Pittsburghers -- let alone we Americans -- are all immigrants, one way or another, and heritage is important to us.

As the title suggests, heritage is the central issue in "Last of the Line." The view of this may be particular to African-Americans -- I'm not sure -- but its larger implications are those we all understand. The play's real conflict takes place not in a larger social group but in the family and, especially and most poignantly, in one person, Gabriel Jameson.

The youngest son of a well-to-do North Carolina family, he has fled from its history in order to make his own way, but as the play begins, he returns, summoned by his older sister and brother, Clora and Alfonso, to face a crisis. Now 42 and broke, he complies, but warily.

The history he has fled is that the family's founding ancestors, his great-great-grandparents, were free slaveholding blacks in the pre-Civil War South. We meet them, Zeb and Cornelia, through flashbacks in which Gabe and his siblings imagine/intuit their lives, based on family traditions. But it's clear that rather than profiting on the backs of their brethren, like Caesar in August Wilson's "Gem of the Ocean," these ancestors bought slaves in order to free them. More, they built their own fortune, Zeb inventing machinery to go into business and even pulling the plow when the mule died.

In a word, they are presented as entrepreneurial saints. I do wish Mr. Williams hadn't sanitized them so much, but I understand he's anticipating controversy, since black slaveholders make for uncomfortable history.

Full of little history lectures and repetition, the play takes a long time to gain momentum and doesn't leap to life until the end of Act 1, when Clora and Alfonso announce the crisis: that the line (they mean the Jameson name) is about to die out, because they have only daughters and are past child-bearing. So it's up to the childless Gabriel to have a son, and they have even picked out his mate, Sylvia, the cute college-educated friend of the family with whom he's been sparring since he arrived home.

The whole audience knows from the start that Gabriel and Sylvia are destined for each other -- their squabbling proves it -- so playwright Williams has to think of ways to delay the inevitable, and he does so with Gabriel's internal conflict.

Which gives me time for my demurral: Why is the line dying out just because the name is? Why can't one of those daughters take the Jameson name and pass it on? This sounds like lack of imagination, disrespect for women or, at least, cultural conservatism.

Nonetheless, that's the premise, and it allows some lively humor of almost the 1930s screwball comedy type. But the play's real heart is in the fine, physically expressive acting of Montae Russell in the lead. Mr. Williams makes him aggressively stupid to start, to increase what conflict there is, but time and again Mr. Russell takes a repetitive moment and jolts it into life. And he gives the play its signature scene, a drunken soliloquy in which he explores his own weakness in the family graveyard. It's achingly real, top-notch writing and acting to match.

His union with Sylvia is secured when she finally shucks her jeans for a robe reminiscent of her forebears, although the effect is compromised by what seems to me to be cheesy lingerie where something simple would have greater impact.

Bria Walker's natural realism and comic touch as Sylvia prove a fit match for Mr. Russell. Vanessa German gives gravitas to the great-great-grandmother, and Kevin Brown and Brenda Marks frame the central story as Alfonso and Clora.

Mark Clayton Southers directs, and Shaun Motley and the other designers and technical staff provide a large, convincing set.

Assuming the play has a future, it mainly needs trimming. You could cut 10 minutes of repetition out of Act 1, and the actors could trim further with crisper transitions, especially in the difficult overlapping of the flashbacks.

Still, this encounter with both daunting past and insecure present has power. And in Mr. Russell's performance, fine writing meets great acting.