The dependence of (1-14C)-palmitate uptake in adult rat heart single cells on albumin was investigated. The apparent initial rate of palmitate uptake vs total palmitate concentration exhibited saturation kinetics, provided the concentration ratio of palmitate vs albumin was kept constant. However, if total palmitate was increased at constant albumin concentrations, the dependence of the initial rate on palmitate concentration was linear. Within the concentration range of total palmitate investigated in this study, the concentration of free palmitate remained almost constant. These results favour the hypothesis, that palmitate uptake in rat myocardium may be mediated by an albumin dependent sarcolemmal transport system.