Walgreens has filed a complaint against Theranos.
The lawsuit was filed Tuesday in Delaware's district court. Walgreens has requested to the court that the documents remain sealed.
Walgreens, once Theranos' biggest partner, terminated its relationship with the blood-testing company in June.
Citing Theranos' decision to void two years' worth of test results and a government agency's rejection of the company's plan of correction, Walgreens on Sunday said its relationship with Theranos was over effective immediately.
The termination shutters an additional 40 Theranos Wellness Centers, where people can go to have their blood drawn, in Walgreens stores.
Walgreens declined to comment beyond what was filed.
More to come.