PARIS — Grousing about the difficulties that come with taking over an old house is old hat. Still, being the new guy is never easy. Two designers gave it a go this season — Alber Elbaz at Lanvin and Laurent Mercier at Balmain — each showing his debut collection on the same day. As most fashion followers will remember, Elbaz is the guy who revived Guy Laroche a few years back and has done brief stints at Saint Laurent and Krizia Top. On Sunday, in honor of Jeanne Lanvin’s sensible clothes, he showed rough-edged wooly jackets and skirts and a smart chocolate suede wrap dress, while, to celebrate Lanvin’s way with draping — and his own — Elbaz sent out a slew of romantic dresses in grayish brown tulle.

Since leaving Yves Saint Laurent in 2000, Elbaz has been traveling and keeping his fashion wits nimble, sketching over 2,000 fashion illustrations during the hiatus. His first Lanvin collection was packed with almost as many ideas — cave-girl furs, arts and crafts dresses, slouchy masculine suits — too many ideas, in fact, and not all of them representative of the designer’s best work. Still, Alber is no babe in the woods, and he’s sure to develop a smart look for the house.

Laurent Mercier’s Balmain collection, however, didn’t instill quite as much confidence. Mercier worked at both Jean Paul Gaultier and Escada, made stage clothes for Lenny Kravitz and has even done a line of his own. Lenny’s flash showed in a hot-pink-and-orange chiffon trapeze dress, while the tailoring skills Mercier exercised chez Gaultier kept his wrapping jackets and chiffon cardigans sharp. But what was with the electric fan appliqued to the back of his riding coat or images of tea sets cluttering up a blouse? The Balmain look needs some real definition. A good starting point might be the gorgeous, graceful couture collections Oscar de la Renta does for the house.