WASHINGTON (CNN) - The Supreme Court has allowed a lawsuit against the makers of the Agent Orange herbicide to continue, despite a nearly two-decade-old class-action settlement.

In two unusual split decisions, the justices Monday granted a Vietnam veteran the right to continue pursuing claims that he was not properly represented in a 1984 settlement involving Dow Chemical (DOW: down $0.35 to $31.65, Research, Estimates), Monsanto, and other chemical manufacturers. But a second vet's claim was set aside for a lower court to re-examine the case.

At issue was whether veterans shut out of the old settlement had a right to make new illness claims, and whether businesses should continue to be held liable for a potentially unlimited period.

In an unsigned opinion, the court allowed Daniel Stephenson and his family to continue his lawsuit against Agent Orange makers. Stephenson is a retired helicopter pilot who served in Vietnam from 1965 to 1970. He was diagnosed with bone marrow cancer five years ago.

The nine-member court split in its decision 4-4. The tie vote essentially affirmed the federal appeals court decision giving Stephenson the right to sue. Justice John Paul Stevens did not participate. No reason was given, but his son was a Vietnam vet who reportedly died from cancer in the mid-1990s.

But in a separate claim, the justices declined to rule on the case of Joe Isaacson, instead ordering a lower court to reconsider his claims. Isaacson, a New Jersey teacher, served at an air base where Agent Orange was used from 1968 to 1969.

Agent Orange was sprayed from U.S. aircraft during the Vietnam War to clear forest and undergrowth, in an effort to expose enemy positions hiding below.

The two veterans in the case claim their due process rights were violated in the original 1984 settlement. The chemical companies agreed to pay out $180 million claims, but for only a 10-year period ending in 1994. Lawyers for Stephenson and Isaacson told the justices during arguments in February that the men only learned of their illnesses after the settlement expired, essentially shutting them and their families out of any monetary compensation for death or disability.

But the court in issuing its ruling did not answer a key question in the case: whether those who did not participate in a class action lawsuit can later claim they were not adequately represented.

Veterans groups had supported the two men, calling it an injustice. Business groups supported the chemical companies, saying reopening settlements would discourage people from settling in the first place.

The case is Dow Chemical versus Stephenson (02-0271).