U.S. law generally prohibits a federal employee from representing an outside party before a government agency. In building a career as an influential government scientist, Walsh has served as both a paid and unpaid advisor to pharmaceutical companies and has helped lead clinical trials that tested the effectiveness of their products. With his help, the companies have brought new antifungal drugs to market, but controversy has flared over whether results from two of the studies were misleading and whether some of the participating patients received adequate treatment. In written comments for this article, Walsh said his advice to industry did not conflict with his position at the NIH's National Cancer Institute, or affect his scientific judgment. "I am not and have never been a representative of, or advocate for, any pharmaceutical company," Walsh said. Two drug makers involved with his federal research, Merck and Pfizer Inc., said they have paid fees to Walsh.