Mr. Rosenstone was 68. The cause of death was pulmonary failure, Phyllis Wender, his partner in Rosenstone/Wender, told the Times. Their New York-based agency was founded in 1981.

Mr. Rosenstone's clients included playwrights David Mamet (Glengarry Glen Ross), Wallace Shawn and Donald Margulies (Dinner With Friends); director and choreographer Graciela Daniele; and playwright, lyricist and composer William Finn (Falsettos). Mamet and Margulies were Pulitzer Prize winners.

"I was Howard's client for much of the last 25 years," Margulies told Playbill.com. "Given his profession, he was a remarkably uncynical, preternaturally sweet man. Howard was, in every sense of the word, an enthusiast. I've lost not just an agent but a great champion and friend."

Mr. Rosenstone was born in Paterson, NJ, and raised in Suffern, N.Y. He attended Syracuse University and the University of Grenoble in France. His career began in the mailroom of the William Morris agency.

He rose to be an agent there. Mr. Rosenstone is survived by his companion, John O'Connor, and a sister, Elaine Auerbach, of Roxbury, NY.