A U.S. soldier wearing a gas mask drinks water as he participates in a decontamination training in South Korea, May 16, 2013. Before 1975, thousands of troops were used for experiments on the effects of various chemical and biological weapons. (JUNG YEON-JE/AFP/Getty Images)

The U.S. government must notify veterans used as human guinea pigs – for tests involving dangerous substances and illegal drugs – as it becomes aware of information relevant to their health, a judge ruled last week.

U.S. District Judge Claudia Wilken's ruling may end a class-action lawsuit filed on behalf of test subjects in 2009. Wilken issued a summary judgment refusing the plaintiffs' request for government-funded private health care, but granted their request for disclosure on possible health concerns stemming from the tests.

"The class of the test subject veterans is fairly large, even though it is aging," attorney Eugene Illovsky, who represents the plaintiffs, including Vietnam Veterans of America, told U.S. News. "It may contain tens of thousands of individuals."

The exact number of soldiers used as test subjects is difficult to determine. Information on the experiments, which reportedly ended in 1975, was classified for years. All subjects reportedly signed consent forms.

"Some folks got multiple substances, " Illovsky said. He added that veteran groups dispute the government's claim that it adequately informed subjects, before or after the tests.

The government has 14 days from July 24 to appeal Wilken's ruling. Vietnam Veterans of America has not publicly commented on the decision.

A 2003 report released by Robert Roswell, then undersecretary for public health with the Department of Veteran Affairs, said declassified information revealed at least 740 soldiers were exposed to the nerve agent VX, 571 to hallucinogenic drugs - such as LSD, PCP and synthetic cannabis analogs - 256 to the chemical sarin and 147 to mustard gas between 1950 and 1975.

Experiments also exposed troops to nuclear radiation and the biological warfare agents Coxiella burnetii, Francisella tularensis and Staphylococcal Enterotoxin B, according to the report.

"[B]etween 1950 and 1975, about 6,720 soldiers took part in experiments involving exposures to 254 different chemicals" at an Army lab in Edgewood Arsenal, Md., the report says.

During World War II, more than 60,000 troops were used for chemical warfare studies, according to the VA report.

"Most of the soldier volunteer subjects of these experiments conducted by the U.S. military were told at the time that they should never reveal the nature of the experiments, and apparently, almost to a man, they kept this secret for the next 40 or more years," the report says.

Illovsky says it's unclear when the legal fight over disclosure will end. "We plan to fight on as hard as we can and as long as we can," he said.