When medical practitioners act as expert witnesses for the plaintiff in contested illness lawsuits, they can be stigmatized by their professional community. Drawing on ethnographic research surrounding the condition multiple chemical sensitivities (MCS) in Australia, this article focuses on: how plaintiff experts specialize; their rationale for deviance from the professional norm; and structural constraints to medical advocacy. By diagnosing and treating the condition as organic, these experts oppose the accepted disease paradigm of the medical community and therefore face professional isolation and peer pressure. They rationalize their continued advocacy within a moral discourse, which includes a professional aspiration toward altruism, an ethical commitment to "truth," and the explicit emphasis that financial gain is not a motivation. For their deviance the experts have been confronted with professional disillusionment and emotional drain. Ultimately, the medical profession is disenfranchising experts who may be vital characters in the quest for understanding about environmental illnesses.