Adenosine is a hormonal modulator of metabolic processes. In some tissues the effect of adenosine on glycolysis is well established. Nevertheless, there are controversial data in heart. We believe that these discrepancies in the literature are due to haemodynamic factors which are not unified in those reports. We studied the direct effect of adenosine in cardiac myocytes in culture, isolated from neonatal rat heart, which are not influenced by haemodynamics forces as whole heart. Myocytes were isolated using conventional methods. Glycolysis was measured following the formation of tritium water from D-[3-3H]glucose. The results obtained showed that the nonmetabolizable adenosine analogue, N6-(L-2-phenylisopropyl)adenosine, (10 microM) stimulates basal glycolysis (49.86%). This effect was observed in the absence or presence of (5 mM) glucose. In separated group of experiments we examined different concentrations of N6-(L-2-phenylisopropyl)adenosine, (1, 10 and 100 microM, glucose 5 mM). Concentrations of 1 y 10 microM of the adenosine analogue stimulated glycolysis in a concentration-dependent fashion, however 100 microM of N6-(L-2-phenylisopropyl)adenosine inhibited glycolysis by 83% possibly through a toxic effect on the myocardial cells. The natural agonist adenosine, (100 microM) also stimulated glycolysis but with less potency. Stimulation of glycolysis by insulin (1 microM) or isoproterenol (1 microM) was potentiated by N6-(L-2-phenylisopropyl)adenosine. We concluded that adenosine stimulates basal or stimulated glycolysis in the myocardial isolated cells. It could be of benefit for the energetic economy in situations were the nucleoside is released.