Subjects working in or living near informal gold mining and processing in southern Peru were studied to determine mercury exposures from two tasks: amalgamation and amalgam smelting. The authors collected 17 airborne and 41 urinary mercury levels. The mean urinary levels were 728 (range: 321-1,662) and 113 (45-197) μg/L for working in smelters and living near smelters, respectively. A third group working in amalgamation had a mean 18 μg/L (range 8-37). People living in the mining town but with no mining activities had 8 μg/L (5-10), while a control group outside the town had 4 μg/L (2-6). Mean airborne mercury exposure was 2,423 μg/m3 (range 530-4,430) during smelting, 30.5 μg/m3 (12-55) during amalgamation, and 12 μg/m3 (3-23) in the mining town. Smelters are highly contaminated with mercury, as are the people living around smelters.