In 1986, the firm merged with Reuben & Proctor, but maintained its name. Isham represented several major business clients including Commonwealth Edison, McDonald's, NBC, and CBS. Former Illinois Governor Richard B. Ogilvie became a partner after he returned to the private sector. On April 20, 1988, the firm dissolved following complications from the merge. At the start of the merge, 225 attorneys worked under the Isham name. By the end, only eighty remained. It was the second-oldest legal firm in Chicago after Sidley Austin. Several of its attorneys left for Sonnenschein Carlin Nath & Rosenthal after Isham disestablished. It was thought to be the second-largest dissolution of a law firm after Finley, Kumble, Wagner, Underberg, Manley, Myerson & Casey.