Xoma Corp. announced that its chairman, Steven...

Xoma Corp. announced that its chairman, Steven C. Mendell, has resigned “to pursue other bioscience interests.”

The Berkeley-based biotechnology company said John L. Castello, its president and chief executive, has succeeded Mendell as chairman. Mendell will remain on Xoma’s board.

Mendell, 51, joined Xoma as chairman, chief operating officer and director in 1984, and became chief executive in 1986. He will become president and chief executive of Prizm Pharmaceuticals, a private, development-stage company in San Diego.