Stern, along with doctors Khristine Eroschevich and Sandeep Kapoor are accused of conspiring to furnish drugs to Smith.
Stern, Eroshevich and Kapoor appeared Wednesday before Superior Court Commissioner Kristi Lousteau. The defendants said "yes" when she asked if they were pleading not guilty.
The commissioner granted a motion requiring each defendant to provide a handwriting sample. She scheduled a June 8 court date to determine when a preliminary hearing will begin.
The former Playboy playmate died after an accidental overdose of prescription drugs in February 2007 at the Hard Rock Casino and Hotel in Hollywood, Florida. She was 39.
Stern, Eroschevich and Kappor were charged in March with six felony counts. The charges were handed down after an investigation that involved the District Attorney's Office, state Attorney General, U.S. Drug Enforcement Administration, California Medical Board and state Department of Insurance.
Stern's attorney said his client "loved Anna Nicole with all of his heart and would never have done anything intentional to harm her."
Attorney Steve Sadow criticized the two-year probe. He said California Attorney General Jerry Brown has "maliciously and viciously labeled Anna a drug addict knowing full well that it's legally unsupportable" under California law.
Sadow suggested the attorney general filed the case merely to advance his political career. Brown, a Democrat who served two terms as governor beginning in 1974, is considering another run for governor next year.
Brown called the accusations "silly" and "completely out of line."
Brown conducted a news conference in February to announce the charges, which were actually filed by county prosecutors.
"Anna Nicole was dead from multiple chemicals put into her body. That's the tragedy and for the defense lawyers to try to exploit that for their own purposes is shocking," Brown said. "These people are whistling in the dark if they think this accusatory rhetoric is going to save them."