The activity of erythrocyte amino levulenic acid dehydratase (ALA-D) and liver and bone lead concentrations were measured in 141 wild rainbow trout from two highway-influenced and two pristine streams. A significant relationship between ALA-D activity and liver lead concentrations among streams (r = 0.157) was observed. However, this relationship was opposite of expected. Trout tissue lead and stream-water lead concentrations were lower than most concentrations observed for control laboratory trout. At these low tissue and water lead concentrations observed in the present study, ALA-D activity cannot be used to document exposure of fish to environmental lead. Other significant correlations with the activity of the enzyme included: trout length (r = -0.411); trout age (r = -0.385); and sediment lead (r = 0.093). Erythrocyte ALA-D activity significantly varied due to sampling period. However, reasons for this deviation cannot be explained from the present study. Multiple regression techniques revealed little concerning trout liver lead concentrations and ALA-D activity relationships. Like ALA-D activity, liver lead concentrations were deemed a poor indicator of organisms' exposure to environmental lead. Bone lead concentrations were the best indicator of environmental contamination. However, the best regression model, which regressed water lead on bone lead, explained only 20.6% of the variation in bone lead burden. In both roadside streams, water lead was positively correlated to turbidity and area precipitation. Water lead concentrations were also positively correlated to discharge in one roadside stream. / M.S.