Civ. Code 51.9 prohibits sexual harassment in business, service or professional relationships, carrying over FEHA’s ban on workplace sex harassment into this different context. As under FEHA, sex harassment can consist of quid pro quo harassment or hostile environment harassment. Here, plaintiff alleged enough to allow a reasonable inference that the women’s soccer coach subjected team members, including plaintiff, to hostile comments and treatment because of their gender, thus stating a claim under section 51.9. However, plaintiff did not state viable claims for negligence, breach of fiduciary duty, or fraud.