Nestling American kestrels (Falco sparverius) inhabiting nest boxes placed throughout the Anaconda Smelter Superfund Site, Montana, were monitored for reproductive success and growth over two successive breeding seasons. A gradient of decreasing soil contaminant concentrations occurred with increasing distance away from the smelter stack. The contaminants of concern (COCs; arsenic, cadmium, lead, copper, and zinc) were determined in food items, pellets, fecal/urate, blood, kidney and liver tissues. Hepatic and renal porphyrin profiles were characterized, and erythrocyte ALAD inhibition assessed, for use as indicators of health effects. Site wide in 1999,43 chicks hatched (81%) with 41 surviving to fledging age (95.3% fledging efficiency). In 2000, 34 chicks hatched (59%) with 32 surviving to fledging age (94% fledging efficiency). Nestling growth and demographics did not appear related to tissue contaminant levels. Active boxes were grouped into two site types (Smelter HiU and Opportunity Ponds) based on their proximity to the smelter site. In 1999, Smelter HiU birds had higher blood lead, liver cadmium, lead, and copper, and kidney cadmium. In 2000, only blood samples were collected, with notably increased lead and cadmium from Smelter Hill birds. Inhibition of erythrocyte ALAD activity at the highest blood lead concentrations indicated lead concentrations reached a threshold level sufficient to initiate biochemical effects. An increase in liver 4-carboxyl porphyrin at the highest liver lead levels likewise suggested sufficient exposure to initiate disruption of heme synthesis. Food items were collected from each active nest. COC concentrations were higher in samples from Smelter Hill boxes, with notable increases seen in arsenic and lead. Contaminant levels in food items were sufficiently high for accumulation in nestling tissues, with elevated levels occurring in nestlings closer in proximity to the smelter.