In the present study, the relationships between -adrenergic receptor (-AR) expression and aerobic capacity evaluated by maximal oxygen consumption () and oxygen consumption level at ventilatory threshold (O₂@VT) were investigated. Seventeen physically untrained and 25 trained men participated in the study. After supine resting, the peripheral blood was sampled for preparation of lymphocytes, the model cell used to analyze the -AR state. The total number of -AR in lymphocytes (-AR_total) was inversely correlated with the O_{2 max} (r = 0.368; P < 0.05) and the O₂@VT (r = 0.359; P < 0.05). Similar relationships were also observed between the number of -AR in cell surface and both O_{2 max} (r = 0.491; P < 0.05) and O₂@VT (r = 0.498; P < 0.05). However, no correlation was obtained between the number of -AR in intracellular compartments and either O_{2 max} or O₂@VT. The ₂-AR mRNA level quantified by the use of competitive reverse transcription-polymerase chain reaction was inversely correlated with O₂@VT (r = 0.567; P < 0.05) and positively correlated with -AR_total (r = 0.521; P < 0.05). These findings suggest that the -AR number in lymphocytes is inversely correlated with aerobic capacity. This relationship may be explained by downregulation of -AR, including internalization with subsequent degradation of the receptors and inhibition of the -AR biosynthesis.