Copper feeding studies in rats are generally initiated at weaning. This study examined whether a 6-week feeding of low or marginal Cu levels (0.2 or 2.5 ppm) to rats initially weighing 135 g produced deleterious effects. Controls were fed 8 ppm Cu. Liver Cu-Zn superoxide dismutase activities paralleled Cu intake. Plasma ceruloplasmin activities were very low for both low and marginal Cu consumption. Low but not marginal Cu intake caused a low body weight, high plasma cholesterol level, anemia, cardiac hypertrophy, and a high degree of hepatic plasma membrane injury 24 hours after CCl4 injection (150 microL/kg intraperitoneally [IP]). In summary, low and marginal Cu intakes produced low Cu enzyme activities, while low Cu intake produced pathological symptoms and poor resistance to an oxidative stress.