The 2-aminoisobutyric acid transport in hepatocytes isolated from 3- and 24-month-old rats was studied and some age-related differences were observed. The basal uptake appeared to be almost constant in cells from old animals during the incubation time, while, in the cells from adults, it showed a progressive increase, interpreted as being due to a derepression mechanism. Epinephrine and glucagon increased the transport in hepatocytes from animals of both ages, even if with a slightly different pattern; the hormones increased the Vmax, while the Km was unchanged at each age tested. However, the glucagon-induced increase in Vmax was lower in the older animals. The mechanism of hormonal action appeared to be similar in adult and old rats. In fact the uptake stimulation by glucagon and epinephrine showed a dependence on protein synthesis. The epinephrine effect was mediated by alpha-adrenergic receptors. No effect was exerted by extracellular amino acids on hepatocytes from 24-month-old animals, suggesting a loss of adaptative regulation mechanism with aging. This behaviour was reflected in the kinetic parameters; in fact the Vmax was not modified by extracellular amino acids at 24 months of age, while it appeared to be strongly decreased in the adult.