Contemporary design is ascending in step with the muscular contemporary art market. Following last month’s record-breaking auctions of postwar and contemporary art, more than $40 million worth of glass-topped tables and Z-shaped chairs will have passed through New York’s auction houses by the end of this week. That figure is some $300 million less than the art totals, but it is a steady uptick from last June’s $19 million worth of design sold at three houses and last December’s $24 million total.

“Until not too long ago there were contemporary art collectors whose furniture was all iconic but generic reissues,” the head of 20th-century design at Sotheby’s, James Zemaitis, said. “The furniture design didn’t compete with the art. People are much more willing to blur now.”

That blurring was in evidence last week in Miami, where the inaugural design.05 art fair was launched to coincide with Art Basel Miami Beach. Art collectors crashed the fair’s press preview, eager to assess French postwar works by Jean Prouve and Charlotte Perriand and mingle with honoree Zaha Hadid, whose enlarged white dendrite-like mass filled the atrium of Miami’s Moore Building. “Finally the two worlds are merging,” a New York design dealer, Christina Grajales, said at the fair.

Sotheby’s and Phillips de Pury, in particular, have been including in their design sales more pieces of recent vintage, in which the art-design overlap is clearest. At Sotheby’s today, Forrest Myers’s set of six fuchsia aluminum “fold” chairs (c. 1971-80), estimated at $20,000 to $30,000, is perfect for that buyer looking for furniture to complement a Jeff Koons hippo.

Sotheby’s estimates its two sales of 20th-century design and American Renaissance will total between $9.5 million and $13.6 million.Mr.Zemaitis noted that in addition to perennial midcentury French favorites such as Prouve and Perriand, buyers are looking for 1970s works in steel and iconic pieces by contemporary designers such as Ron Arad and Droog Design.

Christie’s sale on Wednesday, however, demonstrated the continued demand for classic French mid-century design. Producer Scott Rudin was selling the contents of a country house in a single-owner sale billed as an anonymous private collection. It totaled $10 million, double its presale estimate. The top seller was Paul Dupre-Lafon’s oak and parchment coffee table (c. 1940), which sold for $486,400. The Christie’s multiple-owner sale, which followed in the afternoon, took in $9 million. It was led by a $2 million Tiffany lamp, as deep-pocketed Arts and Crafts buyers blithely ignored the whims of fashion.

Phillips’s 20-21st Century Design Art sale, whose very title emphasizes the slippage between design and art, made $3.2 million yesterday, which was at the low end of its presale estimate. The priciest work was a prototype table by Ms. Hadid made in 2005. The seafoam-green polystyrene and silicone table carried an estimate that would seem low at a contemporary art sale – $250,000 to $350,000. It sold for $296,000.

The modest collection being sold at Phillips yesterday morning by Alexander von Vegesack, founding director of the Vitra Museum, took in $1.1 million, just below its estimate. The artful works made no pretense toward actually being art: They were assembled by Mr. von Vegesack based on the quality of their design innovations.

In the 1960s, Mr. von Vegesack and his avant-garde theater group lived in an Industrial Age, cast-iron factory in Hamburg. Searching for furniture that would match the factory’s sensibility, he discovered bentwood (wood molded by steaming). “Bentwood matched the principle of prefabricated industrial products,” Mr. von Vegesack said.

Some of the earliest bentwood examples, dating back to the 1840s, did not find ready buyers, however. Collectors wanted more contemporary innovations, such as Jean Prouve’s lacquered wood on trapeze table (c. 1951), which dispensed with four legs in favor of two broad steel trapezoids. It sold for $273,600.

On Tuesday, New York newcomer Bonham’s kicked off the week’s design sales with positive momentum, selling $2.4 million of Tiffany, Lalique, and 1930s French Modern furniture, which was at the high end of its presale estimate. Jean Dunand’s round eggshell lacquer table (c. 1922) sold for $534,000, nearly five times its high estimate.The London-based auction house opened its New York salesroom in September. So far, it appears New York buyers have room in the hearts and wallets for another auction house.