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“Most of the time, there is not going to be a dispute about the test,” Mr. Braga said. “There are some that might be worth probing, but by and large these chemists are not going to be testifying in every drug case.”

That would be good news for David Mills, the director of New Mexico’s state laboratory. His lab’s 13 technicians conduct nearly all of the testing for the state’s thousands of drug- and alcohol-related cases.

The analysts already spend considerable time traveling across the state to testify, and Mr. Mills said they’ve seen an increase in subpoenas since the Melendez-Diaz decision.

“We’re able to keep up so far,” Mr. Mills said of the potential impact on lab work, “but as it continues, I think it will cause problems.”

It already has caused problems for Virginia, which had to call a special session of its legislature this month to deal with the impact of the decision.

Immediately after the high court issued its decision in June, defense attorneys began citing it in court. The number of subpoenas to the Virginia Department of Forensic Science in drug cases jumped from 43 in July 2008 to 925 last month.

Prosecutors say they have had to drop or suspend some cases because of scheduling conflicts with the scientists. Also, the increased time the examiners are required to spend in court threatens to worsen a backlog of forensic cases at the state crime lab. The backlog stood at more than 6,100 cases at the end of July.

To avert a potential scheduling nightmare, the state legislature decided to require prosecutors to disclose what scientific analysis they intend to use at least 28 days before trial. The defendant then has two weeks to decide whether to require an analyst to testify. The legislature also allowed prosecutors to ask for delays for scheduling if the defendant wants the analyst to testify.

It still may take time before the full impact of the Melendez-Diaz decision is known.

Matt Kaiser, a Washington federal criminal defense lawyer, suggested that the logic of the decision could be applied in other cases in which documents are introduced into evidence without witness testimony, such as securities fraud or criminal immigration proceedings.

In such immigration cases, for example, documents showing that a defendant has been deported previously are frequently introduced into evidence without testimony from the person who prepared the document.

“I think what it’ll do is create immediate an opportunity for creative and aggressive criminal defense lawyers to try some things they have not been able to try,” Mr. Kaiser said. “There’s language in Melendez-Diaz that allows it to be extended to a lot of cases beyond forensic case.”