A citizen lawsuit alleging damages caused by contamination from Dow Chemical Co. should become a class action, the Michigan Court of Appeals said in a decision released Friday. Those who sued the chemical giant claim that dioxin from Dow's Midland plant got into the Tittabawassee River and contaminated their properties, reducing home values and making homes hard to sell.

The lawsuit seeks to cover anyone who lives in the 100-year floodplain, which could be as many as 2,000 people, the court said.

The case has dragged in the courts since it was filed in March 2003.

"This appeal took two years," said Kathy Henry, one of the plaintiffs. "We're glad about the appeals court ruling, but it's been cruel to make residents wait this long."

A spokesman for Dow said the company is reviewing the opinion.

"We continue to believe that the trial court erred in granting class certification," Scot Wheeler said. "Among other things, the trial court ignored evidence that upwards of one-third of the residential properties sampled showed no contamination."

Since the lawsuit was filed, hot spots of dioxin have been found in the Saginaw River.

An earlier ruling in the case dismissed the residents' demand to make Dow pay for medical monitoring for potential health problems.

Dow contends a University of Michigan study shows that people who live in contaminated areas do not show higher levels of dioxin in their blood than people who don't live near the river.